When instructors talk about “plane” as a player you have to be careful. There are arm planes and shoulder planes etc etc etc. when I think of plane I teach shaft plane. Unless you are Bryson D every club in your bag has a different shaft plane. It’s like that on purpose because it contributes to proper gapping between clubs. But quite simply swing plane determines club path. If the face is square at address and the shaft swings perfectly on plane the face stays very square so therefore swing plane is the key to better shots. Two definitions of correct plane…when the shaft is parallel to the target line it should also be parallel to the ground. And when the shaft is not parallel to the ground it should point at the target line! Food for thought! Good golfing!