From the wiki…
The final girl has been observed in many films, including The Texas Chain Saw Massacre, Halloween, Alien, Friday the 13th, A Nightmare on Elm Street, and Scream. The term was coined by Carol J. Clover in her book Men, Women, and Chainsaws: Gender in the Modern Horror Film (1992). Clover suggested that in these films, the viewer began by sharing the perspective of the killer, but experienced a shift in identification to the final girl partway through the film.
One of the basic premises of Clover’s theory is that audience identification is unstable and fluid across gender lines, particularly in the case of the slasher film. During the final girl’s confrontation with the killer, Clover argues, she becomes masculinized through “phallic appropriation” by taking up a weapon, such as a knife or chainsaw, against the killer. The phenomenon of the male audience having to identify with a young female character in an ostensibly male-oriented genre, usually associated with sadistic voyeurism, raises interesting questions about the nature of slasher films and their relationship with feminism. Clover argues that for a film to be successful, it is necessary for this surviving character to be female because she must experience abject terror, and many viewers would reject a film that showed abject terror on the part of a male.