There have been many movies released through the years that many people consider to be zombie movies. The zombie genre has changed little throughout the years, but one thing has remained. The zombie is a re-animated corpse, bought back from the dead by some natural/supernatural means. While some movies do bend the rules (Return of the Living Dead comes to mind, as it completely abandons being able to kill a zombie by destroying the brain), zombies still remain members of the undead.
Probably one of the most famous movies lumped in with the zombie genre is 28 Days Later. I understand many consider the infected in this movie to be zombies, whilst also crediting it with beginning the resurgence of the zombie genre. But if we take the above definition as what a zombie actually is, the infected in 28 Days Later are certainly not anything of the kind. For one, the infected can be killed by a well placed bullet to the heart. This wouldn't affect a zombie in the slightest. Secondly, the infected are not in any way, shape or form killed by the Rage virus. They are still living, breathing people. Zombies don't feel any emotion. The infected in 28 Days Later are incredibly emotional, beating their victims to death in violent fits of rage, running after their victims screaming in anger. Personally, I cannot think of any single reason why 28 Days Later would be considered a zombie movie, but then again, maybe I am just a horror fan who isn't willing to accept it is a zombie movie.
2007's Rec is another movie that many consider to be a zombie film. This time, a demonic infection spreads throughout an apartment, turning people into crazed killers. The infected in Rec behave in very much the same way as the infected in 28 Days Later do, but this time, they are instilled with the essence of demonic possession which puts them under the control of the Madeiros girl, a young girl who's diabolic situation was used as an experiment to distill the very essence of demonic possession, who has now become a twisted monstrosity that dwells in the penthouse of the apartment. Rec is another movie that I can't understand would be labelled a zombie film. Again, the victims are not killed, but they do seem to have some invulnerability to weapons, something which the essence of demonic possession has bestowed upon them.
1978's classic Romero film The Crazies is also unfairly lumped in with the zombie genre. A military bio weapon turns the residents of a small town into crazed remorseless killers. Not zombies under any circumstances, although in the 2010 remake they may look like them, the crazies of the title are merely the townsfolk driven insane. They are still predominantly human, only with an amplified lust to kill. They still talk, show emotion and even die like regular human beings.
's Shivers, released in 1975 is also widely considered a zombie movie, most probably because of the large group of people that amass in the film, all infected by a parasite that increases the hosts sexual desires and lust to uncontrollable levels. The infected in this movie really do act like zombies, but their intention isn't to feed on their victim. They all reach out with grasping hands, and have the same monotonous moan as many zombies do, but again, they can be killed in exactly the same way as any normal human being. This is a movie where I can actually see why some would consider it a zombie movie, with the mass of bodies moving through the corridors of the apartment, pulling anyone who comes across them amongst them.
2009's Pontypool is an incredibly strange and effective movie, but it is also considered a zombie movie for some reason. A virus is transmitted by the very language we speak, turning people into crazed cannibalistic killers. The movie is effective in it's use of leaving things to the viewers imagination and it's use of sound. Director Bruce McDonald stressed the victims of the virus detailed in the film were not zombies and called them "conversationalists". So even though many would label Pontypool a zombie movie, even by the definition of the director, it isn't.
There are a few other films many consider zombie movies, such as Night of the Creeps, Lamberto Bava's Demoni (that one never fails to surprise me), The Signal, Mulberry Street, French movie Mutantes and even The Evil Dead series of movies.
I guess it all comes down to what the viewer considers the movie to be. We could argue until we are blue in the face, and I doubt anybody's opinion would change on the matter. If anyone else has any movies some consider zombie related but you disagree, please comment below!!