- Animal Motifs: Each House is represented by an animal:
- Gryffindor has lions, strong, powerful and often associated with bravery.
- Slytherin has snakes, cunning, ambitious and sneaky.
- Ravenclaw has (ironically, given the name) eagles, wise, noble and dignified.
- Hufflepuff has badgers, kind, loyal and diligent.
- Color-Coded for Your Convenience: Each house also has its own heraldic colours. According to Rowling, they reflect the house's element in the Four-Element Ensemble.
- Gryffindor: Red and gold, invoking a flame (Fire)
- Slytherin: Green and silver, matching the brackish waters of a lake (Water)
- Ravenclaw: Blue and bronze (Blue and silver in the films), representing the sky and an eagle's plumage respectively (Air)
- Hufflepuff: Black and yellow, representing soil and wheat respectively (Earth)
- Fatal Flaw: The traits that each House possesses can manifest in ways that - if left unaccounted for - can either backfire or lead wizards down a Start of Darkness:
- Gryffindors are preoccupied with honor, making them susceptible to recklessness, zealousness, and glory-seeking.
- Slytherins lack a moral compass to accompany their ambition, which leads to ruthlessness and an undercurrent of supremacy.
- Ravenclaws, with their individualistic nature, have pride and the tendency to backstab one another.
- Hufflepuffs can be too kind, forgiving, and humble for their own good, making them vulnerable to manipulation and generally overlooked.
- Four-Element Ensemble:
- Gryffindor has fire, reflected by its prominent staff member Hagrid, who loves dragons and its common room having a roaring fireplace.
- Slytherin has water, reflected by its head of house Snape, who brews potions and its common room being close to the lake.
- Ravenclaw has air, reflected by its head of house Flitwick, who is first introduced teaching his students to levitate feathers and its common room being in the highest tower.
- Hufflepuff has earth, reflected by its head of house Sprout, who works with magical plants and its common room being underground.
- Lazy Dragon: Hogwarts School's Canis Latinicus motto translates as "Don't tickle a sleeping dragon", alluding to the idea of long-slumbering dragons who may turn fierce when woken up but are otherwise safe to be around.
Created by Harry, Ron and Hermione as a response to Dolores Umbridge's prohibition on teaching students to defend themselves against Voldemort, Dumbledore's Army is the Hogwarts equivalent to the Order of the Phoenix. Its members are Hogwarts students who want to fight Voldemort, and they learn defence from Harry in the Room of Requirement. They communicate using gold coins modified by the Protean Charm to display summons.
Though their activities were interrupted by Dolores Umbridge, Dumbledore's Army remained active in the sixth and seventh books, contributing to the defence of Hogwarts. The organization was named by Ginny Weasley, who said that what the Ministry of Magic would most fear was Dumbledore raising his own army.
- Becoming the Mask: The name was originally just a joke based on the Ministry's paranoia that Dumbledore was using the class to build his own private army. By the time of the seventh book, they're a real fighting force that fights for Dumbledore's values.
- Breaking the Fellowship: Umbridge breaks them apart in Order of the Phoenix, leaving plenty of DA members like Neville a lot lonelier come Half-Blood Prince.
- Child Soldiers: The DA was originally just meant to teach self-defence, but once Hogwarts became the setting for the decisive battle for the Wizarding World, Dumbledore's Army fought alongside real soldiers against the armies of Lord Voldemort.
- Counterfeit Cash: Hermione created fake Galleons to be carried around by every member of the DA. The point isn't to spend them like real money, but to give the DA a covert object that can communicate the date of the next DA meeting.
- Death of a Child: Quite a few members are killed while attempting to fight the villains notably, Colin Creevy, Fred Weasley, and Lavender Brown die.
- Fisher King: Dumbledore's Army makes use of the Room of Requirement, which produces books, targets, and any materials the DA needs on a whim.
- I Was Just Joking: Their name is originally a joke based on the idea that Umbridge refused to train them in defensive magic because she's "afraid that Dumbledore was putting together a private army." When Umbridge finds out about them, however, she takes the name with deadly earnest and, after a while, so do they.
- Kid Hero: The DA trains students from every year to be ready to fight Voldemort, and quite a few them prove themselves against the Death Eaters.
- La Résistance: Initially against Umbridge, but the DA was always formed with the idea of subverting Voldemort's agenda. Once the second war really kicks into gear, the DA is perhaps the best organized force of resistance against the Death Eaters.
- Mildly Military: They may call themselves an Army and actively resist the rule of Voldemort by the seventh book, but they're really just a bunch of teenage students informally acting as teachers and hanging out in an abandoned classroom.
- School Club Front: Dumbledore's Army was formed with this intention (although they weren't keeping its purpose a secret, they weren't exactly openly advertising for members), but Umbridge got wind of it and had a rule allowing her to veto clubs introduced. As a result, it became more of a secret club, the only one openly acknowledging Voldemort's return, and La Résistance in the 7th book.
An informal circle created by Potions master Horace Slughorn to bring together promising young students. Horace selects those who are famous, have famous relatives, or have demonstrated exceptional talent, and interviews them. If they pass the interview, then they are invited to parties hosted by Horace, who also invites alumni who were in the club. This way, he can cultivate connections, ensure that club members become important, and be able to call in minor favours from them.
Members include Horace Slughorn (founder), Voldemort, Lucius Malfoy, Lily Evans, Gwenog Jones, Harry Potter, Hermione Granger, Ginny Weasley, Cormac McLaggen, Blaise Zabini, Neville Longbottom (book only), Marcus Belby (film only), and the Carrow twins (film only).
- Ambition Is Evil: Subverted. The circle is a way for Slughorn to get ahead without directly leading, and getting ahead is the non-bigotry component of the Slytherin credo.
- Dances and Balls: Slughorn holds a Christmas dance with all the Slug Club and guests in attendance. It seems Slughorn even invited some alumni of the club to it, including a real vampire.
- Dark Is Not Evil: Just because it's an elite circle run by a Slytherin doesn't mean it's bad. Lily Potter, nee Evans, was in it and she is one of the nicest people in the series.
- Does This Remind You of Anything?: For fraternities and "inner circles" such as the Bullingdon Club at Eton or the Skull and Bones.
- Initiation Ceremony: Interview with Slughorn, followed by attendance at a party.
- Lighter and Softer: Compared to the other organizations in the series.