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Girls Next Door from WikiPedia:

The cultural and sexual stereotype of the girl next door is invoked in American contexts to indicate wholesome, unassuming femininity, as opposed to the culture's other female stereotypes such as the tomboy, the valley girl, the femme fatale, or the slut. The male equivalent is the "boy next door". An example of each is found in Thornton Wilder's Our Town, in the characters of Emily Webb and George Gibbs; or in Mark Twain's The Adventures of Tom Sawyer series, in the characters of Tom Sawyer and Becky Thatcher.

In the idealised American context, falling in love with the "girl next door" is an archetypal romantic fiction. Unlike the femme fatale, the girl next door does not have hidden plans of her own, because her character and personality are open and straightforward, and because her social, economic, and sexual intentions do not need to be concealed. Unlike the princesse lointaine, she seldom is richer or of a higher social status than the boy protagonist. The girl next door likely is a girl whom the protagonist has known most of his life, but in the past could not appreciate the depth of his feelings for her because of his youth.

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