Mean Aerodynamic Chord (MAC)
MAC stands for Mean Aerodynamic Chord. MAC is the chord through the centroid of a single wing's plan area. A wing's chord can be difficult to measure because only if a wing was completely rectangular is the MAC equal to the chord. Most wing's aerodynamic centers are at 25% MAC. The ratio of the chord of a wing to its span is known as the aspect ratio. Aspect ratio a relative indication of the lift-induced drag the wing might create. In general, planes with higher aspect ratios, as ones with wide, skinny wings, have less drag. This is why high efficiency gliders have such long wings.