Center of pressure:
The upper surface has pressures distributed which produce the upper surface lift.
The lower surface has pressures distributed which produce the lower surface force. Net lift produced by the airfoil is the difference between lift on the upper surface and the force on the lower surface. Net lift is effectively concentrated at a point on the chord called the Center Of Pressure.
The aerodynamic force is applied at a location 1/4 from the leading edge of a rectangular wing
at subsonic speed, the magnitude of the aerodynamic moment remains nearly
constant even when the angle of attack changes.This location is called the wing’s Aerodynamic Centre AC. (At supersonic speed, the aerodynamic centre is near 1/2 of the chord).