a sudden, surprise attack on a place.

a sudden short attack

search without warning, make a sudden surprise attack on; "The police raided the crack house"

a a surprise attack by a small force, or a a daring operation against a competitor

a large scale attack on an area by a group of parties or players

Large-scale attack on an area, usually involving guilds.

A coordinated attack on a given area (usually a dungeon), performed by a large amount of people (usually a guild), organized into individual groups. The purpose of a raid is to accomplish something that cannot be done by a single person or group; usually getting certain drops, or sometimes for the sake of XPing.

A raid is a large-scale attack on an area by a group of players.