Center of pressure: When a fluid flows around the surface of an object, there is a variation of pressure on the surface, due to variation in velocity over the surface. Center of pressure is the average location of pressure on the surface of the object. Aerodynamic forces act through this center of pressure. Aerodynamic forces can be resolved into components of lift and drag. Aerodynamic moment is zero at the center of pressure.

Center of pressure changes with angle of attack

Aerodynamic center:  When an object is moving through air, the velocity of air varies over the surface of the object. These variation of velocity creates a variation of pressure on the surface. The pressure distribution on the object also imparts torque or moment. On changing the angle of attack, pressure distribution and thus location of center of pressure, aerodynamic forces and aerodynamic moment changes.

Aerodynamic moment can be computed at any location on the airfoil, if the location of aerodynamic forces applied is known. However, there is a point on the airfoil, where the aerodynamic moment remains constant with the change in the angle of attack. This point is called the aerodynamic center. So, if the aerodynamic forces act through the aerodynamic center, aerodynamic moment remains constant, with any angle of attack. Aerodynamic center is 1/4 chord for low speed airfoils and at nearly 1/2 chord for supersonic airfoils.

Aerodynamic center does not change with angle of attack