[tepitoperrito]

Is a "ply" a unit I'm not familiar with? Or does it just refer to a single layer. (Honestly not sure and curious)

[seanhunter]

A ply is half a move. Or to put it another way, one move is one ply by white and one ply by black. This is a term that is common to all sequential games.

https://en.wikipedia.org/wiki/Ply_(game_theory)