A zombie apocalypse is a particular scenario of apocalyptic fiction that customarily has a science fiction/horror rationale. In a zombie apocalypse, a widespread rise of zombies hostile to human life engages in a general assault on civilization. In some mythologies, victims of zombies may become zombies themselves if they are bitten by zombies; in others, everyone who dies, whatever the cause, becomes one of the undead. In either scenario, this causes the outbreak to become an exponentially growing crisis: the spreading "zombie plague" swamps normal military and law enforcement organizations, leading to the panicked collapse of civilian society until only isolated pockets of survivors remain, scavenging for food and supplies in a world reduced to a pre-industrial hostile wilderness.

The day that the zombie apocalypse begins is sometimes known, by analogy with military operations such as D-Day, as Z-Day.