Alright, considering Wikipedia is a garbage source anyways, (Proven by somebody editing it today at will) let's look at some other sources.

http://mmoterms.com/mmorpg-terms-r

Raid

A more substantial engagement involving a large organized group of players typically set in a dungeon and involving difficult bosses.
http://www.urbandictionary.com/define.php?term=raid

raid
Often used with mmorpgs. It involves players banding together to succeed at a common goal- such as taking over territory, killing an opposing faction, or most commonly killing big scary internet monsters that drop coveted items.

It can be used as a noun or verb, noun referring a specific event, and in verbage, the act of embarking on that event.
A: We've scheduled a Black Temple raid tonight. You coming?
B: I can't raid, I gotta get laid!
A: No epix or dkp for you!
http://www.mmoglossary.com/mmorpg_terms/1/index.html

- Raid .
A raid is a large-scale attack on an area by a group of players.
So I'm seeing group, not seeing groups. So how exactly does Raid get defined as multi-group content? Oh wait, it doesn't, because you're stating opinions as facts.