The "Live Migrate Your Replica Set to Atlas" documentation page mainly refers to the final step of the migration process as a "cut over". For example:

When the migration timer and the Start Cut Over button turn green, proceed to the next step.

However, this is inconsistent with other references that use "cutover". The "STAGING AND PRODUCTION MIGRATIONS" note on that page states:

Perform a partial migration that stops at the *Perform the Cutover* step first.

And the actual button in Atlas is labeled "START CUTOVER":