Raid

A raid is an ominous event in which waves of various mobs, mainly illagers, spawn and attack a village. It is triggered when a player with the Raid Omen effect runs out of said effect while inside a village.

When a player with the Bad Omen status effect enters a village (see below for exact definitions), the effect converts into Raid Omen. If the player doesn't drink milk to cancel the Raid Omen before it naturally expires, a raid begins.

Raids can be triggered in the Overworld and the End, and in non-Java Edition games, the Nether.[1]