Call of Duty Elite is going away on February 28, 2014 and it's not coming back. The service started with Modern Warfare 3 and gave players early DLC access, clan management, in-depth stat tracking, and the like. Many of these features went free with Black Ops II.
Activision has posted a shutdown FAQ, viewable here, offering specifics. I'll save you the effort by saying that it's a whole bunch of "Go download the Call of Duty Clan Wars app as a replacement." Founding members who logged into Elite since January 1, 2014 will get two hours of Double XP in Call of Duty: Ghosts as a token of appreciation. Thanks, I guess?