It is obtained when one finishes the campaign mission The Covenant on the Normal, Heroic, or Legendary difficulty. In Halo: The Master Chief Collection, it is possible to get this achievement on Easy.
The Halo 3 achievement gives 40 Gamerpoints to the player. It is so named because it is the final level that the player can fight against the Covenant, and is also the level which ends in the total defeat of humanity's bitter enemy. It is represented by a blue plate with the roman numeral for Seven, VII, on it.