Parting the Sea
From Halopedia, the Halo wiki
Parting the Sea is an achievement in Halo: The Master Chief Collection. It is awarded by beating the 30,000 point par score on Exodus in Halo: Reach. Though it can theoretically be unlocked on any difficulty, more points are awarded in campaign scoring when playing on higher difficulties.
The name of the achievement is a reference to the biblical parting of the Red Sea from the Book of Exodus.