The center of pressure is the point along the chord line of an airfoil where of all aerodynamic forces are considered to act.

With a symmetrical airfoil, the center of pressure remains relatively constant with changes in angles of attack.  With a non-symmetrical airfoil, the center of pressure moves significantly along the chord line with changes in the angle of attack.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-7
Principles of Helicopter Flight, 2nd Edition, pg. 22
FM 3-04.203-2007 Fundamentals of Flight pg. 1-7

Other Helicopter Aerodynamic Principles