A "Girl Next Door" is a character who, it is implied, an "ordinary guy" male protagonist might have known when growing up, and who he might like without feeling intimidated. She may literally be from the same neighborhood as the hero, or she may just remind him of girls he knew back home. She embodies an average and "wholesome" femininity. She is neither butch nor overly feminine; she isn't usually promiscuous, and she might act as a foil to a woman who is, such as the "downtown girl" in Town Girls grouping. She is typically prettyin an accessibleway. However, since the trope is essentially about her personality, some Girls Next Door are considered knock-outs. In that case, though, they're probably the local beauty in a neighborhood or small town, rather then being famous for their looks in a wider context — to start with, anyway, though they may advance to fame or stardom in the course of the story.
As the kind of girl that male protagonist might have been friends with all his life, the Girl Next Door is easy to talk to, like a tomboy, but she doesn't force her presence on anybody; she may keep to herself, like a Naïve Everygirl, while not rejecting social interaction. Equally, she may well be a bad boy's fantasy or target, because he finds her "good girl" image a challenge. She has the goodness of the light feminine in Light Feminine and Dark Feminine; she is good and attractive but not vain or arrogant about it. She certainly doesn't give the impression that she's spicy or fiery — at least not obviously so, though she may have hidden depths of some sort. Nothing says that she has to be incapable of passion; she's just unlikely to be extrovert about it.
Often when a Girl Next Door is involved, the story has one of three types of plot: she's the Unlucky Childhood Friend to the male lead (usually a jock); she has a male Unlucky Childhood Friend that is chasing after her; or she is the Betty in a Betty and VeronicaLove Triangle. Occasionally, all three combine in a huge mess. (This set-up was used, more or less, in several movies by John Hughes.) Possibly she is with the main character as a childhood, college, or high school sweetheart, but this isn't always the case.
The Spear Counterpart, Boy Next Door, is pretty much the same only, you know, male. Compare Tomboy and contrast with Femme Fatale and Peerless Love Interest. Also compare The All-American Boy, who might well be her High School Sweetheart.
For the 2004 film, see The Girl Next Door. For Numbuh 3 and Numbuh 5, see Codename: Kids Next Door. Also not to be mistaken for Crystal Bernard's album, The Girl Next Door.
There is an unusual example in Welcome to the NHK. Misaki Nakahara is a literal Girl Next Door whose innocence and rather plain beauty is, at first, an integral part of her relationship with Satou, combining this trope with Manic Pixie Dream Girl. However, both tropes become subverted when she is slowly revealed to exhibit nearly every symptom of a textbook case of Borderline Personality Disorder, including extreme self-esteem issues, self-harm, skewed social perspective, and an unhealthy (suicidally so) obsession with Satou.
Played with in regard to Gwen Stacy of Spider-Man. As portrayed in the comics, Gwen was more of an exotic flower whom Peter only met after he left Forest Hill and "went out into the world", i.e. Manhattan and college. She came from an upper-class background, her first boyfriend, Harry, was the son of a millionaire and in her first appearance she was introduced as a high-school beauty queen. However, as she became the Betty to Mary Jane's Veronica, she moved into this category.
Shellie from Sin City is sassy but meek enough to qualify.
Mary Jane Watson from the Spider-Man Trilogy movies is an example, arguably due to her being a Composite Character with Liz Allan, who in the comics attended Midtown High together with Peter Parker and Flash Thompson.
He's Just Not That Into You has three: Gigi Phillips is like a basset hound. They're kinda pathetic - so you want to cheer them up. Beth Murphy wants a good man and a husband. Mary is a romantic who has been hiding behind technology.
Mary, the protagonist of the movie Saved, is played as one of these; more importantly, she doesn't lose the general demeanor even after becoming pregnant. This is meant to show Mary as genuinely filled with the Christian spirit of compassion, in order to contrast Mary with her Alpha Bitch rival, who attends the same Christian school environment as her but is hypocritical about being "filled with Christ's love".
Sunshine has the titular character the vampire-slaying, magic-wielding version.
Julie Sims in 1632 is a Girl Next Doorwith a rifle. She's described as being pretty, but not much more, and aside from occasional bouts of angst is fairly level-headed.
Ruby, Ralph's girlfriend in Urn Burial has lived in the house next door to him since they were born, and whilst not drop dead gorgeous is plenty attractive enough for being familiar and not having any pretensions.
Bernadette (Bernie) Manuelito in the Joe Leaphorn/Jim Chee series by Tony Hillerman is the rare Native American version. She is a pretty, cheerful, down-to-earth fellow Navajo cop who is contrasted to Chee's previous love interest, the beautiful, sophisticated, half-white lawyer Janet Pete from Washington, D.C.
From Buffy the Vampire Slayer, Willow is straight up this, while Buffy's toughness mixed with her femininity make her character average out.
The first 2 seasons, Buffy is very much this trope, befriending underdogs, having quick come-backs and being especially peppy. She's also naive & somewhat awkward around guys she likes, and Zander is her male Unlucky Childhood Friend. Over time, however, a lot of "break the cutie" occurs, turning her into a 99% Crusader. Willow (who has a lot of the Librarian traits) also turns into a Crusader by the end, having lost her naive innocence along with Buffy.
Monica Geller from Friends is a bossier and sexier version that most, but is down to earth, maternal, and The Heart of the group. She lives across the hall from Joey (who was originally going to be her love interest) and Chandler (her eventual boyfriend and husband).
Mary from 7th Heaven starts going out with a neighbor guy who she used to play basketball with. After she breaks up with him he says that playing a game together will help him feel more like they're friends again.
Penny from The Big Bang Theory. She moves into the apartment across the hall in the first episode and that alone gave Leonard some hope that she might become interested in him. She is consistently portrayed as a fairly down-to-earth and friendly girl who helps fill in the gaps in the guys' social skills. Still, as she and Leonard start dating, it's made fairly clear that if they weren't neighbors he wouldn't have had much of a shot with her.
To some extent, Alyx from Half-Life 2. Only debatable thing is that when she was living in Black Mesa, she was only a baby. But then came the Combine occupation and she became a rather hot tomboy by the time Gordon returned two decades later. Since then, they've been together for most of the time.
Note that all three of these girls are royalty (more or less; Lycia's not a monarchy but Lilina's father is nevertheless the head of a country). Then again, the same is true of their love interests, so it's all relative.
Rachel from Tower of God is set up as this, being a childhood friend and mother figure for Baam. The fact that she ran away from their life together should have been a first good hint, but it is subverted when she tries to kill him out of jealousy and fear that he might stop her in her quest.
In The Fairly OddParents, Tootie is a geeky girl who lives near Timmy and quite obviously loves him. Although Timmy doesn't return her affections at first, he sympathizes with her since they both have to deal with Tootie's meaner older sister and Timmy's babysitter, Vicky. According to the live action movie, many years later, Tootie returns to town a transformed woman, and Timmy falls in love with her.
The fashion industry is forever caught between the ideal of maximum glamour and idealised beauty, and the need to sell stuff to, well, real people. One solution is to employ models with (allegedly) "Girl Next Door" looks; it's said that this becomes more widespread during economic recessions, when the industry is less inclined to take chances. Of course, these tend to be unusually slim, poised Girls Next Door, with perfect complexions.