What is "Legion's Mission in Mass Effect 3?"

Everywhere I look for help in uniting the Geth and the Quarians, I only see Legion's Mission in Mass Effect 3 only referred to as just that: Legion's Mission in Mass Effect 3.

Even here: How do I establish peace between the Geth and the Quarians?

And here: Brokering peace between quarian and geth options don't appear

...it is only cryptically referred to as "Legion's Mission in Mass Effect 3." There is no indication as to the actual name of the quest, when I receive it, and what prequisites there are, if any.

Primarily, this refers to Priority: Rannoch, where the major decision point is between Tali and Legion, and the Geth and the quarians. In addition, Legion's mission also encompasses Priority: Geth Dreadnought, where you first encounter Legion in ME3, as well as Rannoch: Geth Fighter Squadrons and Rannoch: Admiral Koris, both of which can modify the outcome of the decision point. It is for this reason that Rannoch: Admiral Koris is included here, despite the fact that Legion isn't involved in the mission.