What is a raid in gaming?

Answer 1

Basically, a raid is an instance that is harder than a dungeon, and requires more players to complete (10-25). They have better rewards than dungeons and require players to commit over an hour or more to complete. They are usually best completed with a guild, although there are some players who pug (pick-up group) then when they are bored or their guild doesnt want to run anything.

Raids can only be completed once a week.

Answer 2

A raid is when a large group of players, mostly in MMO's (Massive Multiplayer Online), like World of Warcraft, for example, join together in 10 man or 40 man teams to take down bosses in the games.