Final Girl Theory

This theory was put forward by Carol J.Clover in 1992; to be more specific the evidence was already out there she merely connected the dots and coined the term.

The summary of this theory is that there is always a girl who survives at the end to either kill the antagonist or simply out of sheer luck. They're usually the narrator or do the voice over introduction in order to make the story come full circle. They're always a virgin or sexually unavailable; in accordance to the rules of horror set up by Scream (1996). And they'd most often have a unisex name; like Teddy or Sam.

An example would be Halloween (1978); the final girl in this case is Laurie Strode, a hard-working student who rarely ever goes out on dates. So she's a virgin, is sexually unavailable, has a unisex name and survives at the end of the film, all tropes proving she's the final girl in this movie.