It is basically like a BCNM or KSNM in XI.

Basically is an instance where you are warped to an arena to fight a boss. Nothing more or less.

Personally I would not call it a raid, I think of those as large scale areas where you take down alot of enemy and bosses. Similar to Dynamis or the large battles in EQ.

Ifrit is just a party battle against a boss, in a instance away from the rest of the server.