The Nf6 opening move doesn’t really have its own name, except when combined with White’s move. The Black move “Nf6” appears in two main Black opening variations.
Against 1.e4 by White, Black’s 1..Nf6 is the start of Alekhine’s Defence.
Diagram: Alekhine’s Defence with Nf6
Diagram: Indian Defences with Nf6
Black may also play 1...Nf6 against other openings, such as a copycat move against the Reti Opening.