http://en.wikipedia.org/wiki/Raid_(gaming)

"A raid is a type of mission in a video game in which a very large number of people (larger than the normal team size set by the game) attempt to defeat a boss monster."

4/8-man is pretty standard and prevalent throughout the game - Story missions, Primals, basic dungeons use 4/8-man parties.

Coil really isn't a raid. If it wasn't for the trash Coil would be exactly the same as Primal fights.