A (usually female) character's family mistreats them, almost certainly by the use of force, and perhaps sexually (perhaps fatally), to 'restore' their family's 'honour'.
Not honour of the kind an individual earns through decency, dedication, and service, mind you. This is 'honour' with inverted commas - the kind held by entire families, that can only ever be tarnished, and the tarnish-ers of which one must always always discipline or humiliate for fear of losing even more 'honour'. This kind of familial humiliation is often the result of the selfish actions of wayward children who are not mindful of their place in the familial heirarchy (at the bottom, firmly under the heel of the elders/patriarch).
Selfish actions like, say, having a lover/spouse-to-be that (for whatever reason) mummy and daddy don't approve of, or refusing an Arranged Marriage. Maybe, worse still, they've shown their complete lack of gratitude to and love for their parents and their culture by changing religion, or being homosexual (shock-horror!)! Or perhaps they're just not 'phoning home enough, and trying to be all modern and independent and stuff (no age limit on this one, mind, it lasts until 'you' [or your sibling/partner] head the family). Or perhaps they have, again, shown the extent of their contempt for their family and culture by getting raped.
The trope includes, but is not limited to, so-called "honour killings" wherein the victims' families actually go so far as to, you guessed it, murder their wayward family children/family members (and probably try to cover it up). If they get caught in a Western society, expect them to be stunned at the authorities prosecuting them to the fullest extent of the law with the sentencing judge telling they are dishonorable scum to make it real clear to everyone that this crime will not be tolerated.
While this kind of violence is usually directed against female relatives (inclusive of targeting the men they court), it does go both ways, especially when it comes to homosexuality.
Honor Related Abuse is bit odd because... well, it sort of goes against the natural instinct to, you know, love and be loving to your family. It has in any case given us some hilariously psychotic statements along the lines of 'we had to lock them in the cellar for twenty years/beat/rape/kill them because it was for their own good/we loved them'. While it's fairly typical of pre-modern societies (like pre-19th/20th century Europe), the value systems that make Honor Related Abuse look like a jolly good idea seem a bit... dated now that we believe that nobody has the right to do certain things to other people. This is particularly jarring when it comes to the whole 'rape victim = Defiled Forever' thing. To people with modern sensibilities it's all just a teensy bit repulsive.
Contrast Rape and Revenge, where the victim is considered a protagonist rather than a passive object to discard for no longer being "clean."
Happens far too often in Real Life. Let The Other Wikiprovide Real Life facts, and leave it at that.
The movie Not Without My Daughter (as well as the book it's based on) tells the story of a failed marriage and a custody battle as entirely a matter of Honor Related Abuse. The characters start out as an American family, although the husband is of Iranian descent. They are happy with each other until they visit Iran, and the husband's relatives there can start putting much more pressure on him than they could long-distance. In his new-found role as protector of the family honor, he starts battering his wife and brainwashing his daughter. While the wife and daughter are victims of the husband-turned-monster, he is also clearly portrayed as a victim of his own (even by Iranian standards) ultra-conservative family.
Since the daughter has been given Iranian citizenship (without the mother's consent), the mother can't even try to take her back to America without risking the death penalty. Eventually, they manage to flee the country and return home to the USA.
In Stoning of Soraya M., this is the excuse for the titular stoning; The husband wants to spend more time with his mistress and avoid the cost of a divorce, so he first sends his wife to do household chores for a male widow and then accuses her of adultery. They eventually bully the widower to falsely testify against her and force Soraya's father and children to participate in the stoning.
In the film When We Leave, a young woman leaves her abusive husband in Turkey to return to her family in Germany. Although basically sympathetic to the abuse she has endured, they are ashamed of her for leaving her husband and supposedly bringing shame onto her family — their friends shun them and her younger sister's fiance nearly ends their relationship until the father offers the family a large sum of money. When the young woman flees the family apartment after realizing that they are planning to kidnap her son and send him back to his father, they shun her outright and her brother begins stalking and harassing her, culminating in him trying to stab her (after her younger brother can't bring himself to shoot her) and accidentally killing her son, who she was holding in her arms at the time. Ironically, despite having no remorse about trying to kill his own sister, he is horrified at having killed his nephew.
In the movie Crossing Over, a Middle Eastern man murders his sister and her lover, incensed at her refusal to end her affair with a man who is not only married, but Mexican.
There is a similar story in Arthur Conan Doyle's The White Company; a French peasant father and daughter tie themselves together and jump into the mill pond to drown after the girl attracts the lustful attentions of a nobleman.
Also in Livy, Lucretia did thisto herself when she was raped by the son of King Tarquin; this supposedly set off the revolution against the monarchy and the establishment of the Roman Republic.
This also happens in Shakespeare's version (a lengthy poem) The Rape of Lucrece.
The Swedish book Mordet på Fadime (The murder of Fadime) revolves around this, especially the case that made "honor killings" a well known concept in Sweden.
Flowers In The Attic, the book and film. A widow with children tries to restore connections with her wealthy family, but she was estranged due to Brother-Sister Incest. After she takes enough punishment to satisfy their demands for penance, she abandons her imprisoned children to their continued abuse.
The Empire trilogy includes several instances of honorable suicide, and at least one character "honor kills" his entire family prior to such an act. Many deaths are arranged so that rivals can "gain in honor." The majority of people who have the misfortune of being slaves are treated as poorly as possible so that their "debts" may be paid and they can go honorably to death and to their next life. In fact, much of the trilogy is just made of this trope.
In Buffy the Vampire Slayer, Tara's family is like this. They abuse her emotionally and lie to her to make her hate herself, fooling her to believe that she is less than human. When she breaks free to make a life of her own, they start threatening to move on to physical abuse, and would most likely have made good on their threats if it wasn't for almost the entire cast closing ranks around her and telling them that they would have to go through them to get to her. Except Spike. Spike does help, in his own unique fashion: he hits Tara in the face. Since it triggers his Morality Chip, thus proving she's entirely human, it does help her... by hurting her. And him.
Basically the whole plot of the Law & Order: Special Victims Unit season two episode "Honor." A woman is brutally killed, and it turns out it was related to her family's disapproval of her boyfriend. Her mother finally steps up and admits what she saw and...well, you try getting those final images out of your head.
Said images being her corpse in the bedroom of her home, her husband having slashed her throat and fled back to Afghanistan before the police could catch him, with his characterization of the episode making it clear that he won't lose a moment of sleep over having murdered his supposed love and his own child.
While the killing wasn't premeditated, the argument was still mostly about Macton's Fantastic Racism against his brother-in-law.
A storyline on the soap opera Port Charles had a young Middle Eastern woman being terrorized by her brother. She had fled her country after being raped and her family responded by sending her brother to kill her in order to restore family honor. This being a soap opera, a well-meaning friend quickly married her to keep her from being deported back to her country as well as to pacify her family. Unfortunately, it didn't work—the brother continued stalking her and discovered that the marriage was fake (the man already had a girlfriend) and eventually did attempt to kill her, though he was unsuccessful.
Subverted in The Closer two-parter "Living Proof". A scuffle between two Albanian men in a mall ends with the older one dead, the younger one claiming he only killed in self-defense (reasonable enough, as the older man had pulled out the knife in the first place). He claimed that the old man was his father, who had disowned him for marrying a Christian. Then the dead man's daughters turn up dead, and the son suggests that his father had snapped and gone on a belated honor-killing spree against his family (the daughters for being raped by Serbian forces during the Albanian genocide, the son for failing to protect them and surviving by hiding). In fact, the "son" was one of the murdering Serbian soldiers, pulling a Dead Person Impersonation using the name of one of his victims to escape trial for war crimes. Unfortunately for him, his stolen identity's father met him by chance, and the man tried to kill the entire Albanian family so they couldn't out him as a war criminal.
Sometimes referenced on Goodness Gracious Me. One example was a mock advertisement for the fire-proof "Asbestos Sari", designed to prevent the wearer meeting an untimely death in a "kitchen accident" (this is sometimes used as a euphemism for women being killed over dowry disputes.)
Frank's subplot in one episode of Blue Bloods concerned a Turkish violinist on a US tour seeking political asylum due to her having dated an American during the tour: she believed she would be in danger of an honor killing if she returned home. The State Department vetoes it for political reasons, so Frank works his contacts and gets the New York Philharmonic to hire her, and State agrees to get her a work visa.
Parts of The Bible command honor killing for alleged sexual misconduct. In Leviticus 21:9 of Old Testament, a Levite's daughter is to be subjected to honor killing if she becomes a prostitute. Deuteronomy 22:13-21 commands that a female is to be stoned to death if she is suspected of not being a virgin on her wedding night. Even before those laws were written down, in Genesis 38:24-30, Judah calls for Tamar to be burned to death for becoming pregnant out of wedlock through prostitution. In a Shocking Swerve, he spares her life, because she reveals that he is the father, and she only impersonated a shrine prostitute because he was trying to weasel his way out of a levirate marriage. He even goes on to say that in doing what she did (thus fulfilling her duty to carry on his family lineage), she is more righteous than he is.
The Bible contains laws specifically against fornication (aimed at both sexes) and against prostitution, so the laws aren't strictly family-honor related as much as being part of the general law. Deuteronomy 21:18-21 details how a stubborn son, who drinks, is rebellious, and otherwise dishonors and disobeys his family should be dealt with (by stoning) if his family can't control him.
The protagonist of Titus Andronicus. After his daughter Lavinia gets raped, he restores his honor by murdering the rapists — and her! Sure, she was depicted as a severe case of Defiled Forever, but if the murder had been done in a gentler way it could have been considered a Mercy Killing to put her out of her misery, considering what else the rapists did to her — but the way he did it (at least in the movie version, and that one stays true to the original manuscript) was definitely a part of his own personal revenge.
The original manuscript only had him killing her; in keeping with Shakespearean stage directions, it gave no specifics about how the act should be carried out, making this highly subjective.
Plus, the way it was presented and her actions throughout the movie strongly implied that Lavinia agreed to him him killing her and didn't want to live with her shame. Plus, it wasn't just Titus's revenge. Lavinia pleaded with Tamora to kill her rather than let her son's rape her, but Tamora orders her sons to ravish her anyway. So Lavinia being killed in front of Tamora and the Emperor (thus requiring Titus to explain himself) fits her revenge as well.
How about his son, Mutius? When Bassianus runs off with Lavinia after Titus promised her hand to Saturninus, the new emperor, the rest of his sons help them. When Mutius stands in his way, Titus cuts him down without a second thought.
The Desert Song has a variant. The Mighty Whitey hero is left to die in the desert and loses his leadership of his band of outlaws due to refusing to fight an opponent.
Melusine (an anthropomorphic dolphin) in Concession was murdered by her brother-in-law for getting impregnated by a land-dweller. Prompting the father to destroy an entire city and her to come back as an insane ghost.