Well....the only way to find out what it is is to activate the game...

It's a dlc, which you can't activate till you have the original game.

If you intend to use that key for yourself you shouldn't post it publicly here.. edit it if you do intend to get the game that DLC is for and use it later..

If it was actually for black ops 1 some ninja probably already use it... and if it is for a DLC from the game the most probable is that the key is already used by ninjas too xD dont post your keys on the forum unless you want to give it away...

On other hand, Steam support can actually tell you what game is that key from... you can contact them and ask :), you should also contact the facebook page that gave you the key since they actually didnt gave you the right one, (the response from steam support saying what game is the key could help you in that, i had a problem with gmg once and with gmg support and steam support i was able to fix it)

EDIT: You can edit your original post clicking the open button on the right top part of the page, i recommend you to erase the key from the post

It seems to be the Call of Duty: Black Ops Annihilation Content Pack
(no clue if it is taken by now or not)

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We have to go back to the island Vodainstalater!

It's for what he said.

Looks like somebody took it but didn't thank you. :(