Remnant

Did you mean the original Halo 2 multiplayer map, Relic, or another use of the word?

Relic Anniversary is a remake of the classic Halo 2 map Relic, to be released for Halo 2: Anniversary. It, along with the campaign of Halo 3: ODST and an additional nameplate and emblem, are to be given to all players who have played Halo: The Master Chief Collection between its launch and the 19th of December 2014. It will be available, along with the rest of the rewards, in spring 2015.