Here’s a quick write-up of one classic example — — which is often available as a full movie on public domain platforms. Night of the Living Dead (1968) – Write-up
Synopsis: A group of strangers takes refuge in an isolated farmhouse as hordes of the undead — slow-moving, flesh-eating "ghouls" — surround them. As the night goes on, panic, paranoia, and limited resources turn the living against each other more than the zombies do. zombies movie full movie
It sounds like you're looking for a , but you didn't specify a title. Here’s a quick write-up of one classic example