Apex refers to the point of the corner
In formula 1, a corner is much more than a turn on the track, it is a considered and deliberate... There's more... where the car comes closest to the inside of the track and the transitions from entering the corner to exiting. The location of the is determined by the race line of the car.
Drivers may take slightly different lines but hitting the apex perfectly is a key part of moving through the corner at maximum speed.
