OPEN FACE
Open face refers to the position of the clubface relative to the target line at impact (the moment the clubface strikes the ball). However, with an open face (a.k.a., a club that is open at impact), the toe of the club is turned a little rearward. The toe of the club is a little behind the heel at impact. So the angle that is 90 degrees when the clubface is square is more than 90 degrees with an open face.
This term leads to a slice or push and is easily confused as being the same as those two terms.