Phase Line Alpha

From Halopedia, the Halo wiki

Phase Line Alpha was a United Nations Space Command-defined boundary in the space surrounding Saturn's second moon, Enceladus at the end of the Human-Covenant War. Following the short Battle of October 10 and the loss of the UNSC Totem Lake, the Third Fleet's Battle Group Rhino retreated and regrouped at Phase Line Alpha above Enceladus.[1]