Answer by Thomas Zerbarini:
The simplest answer is that a high aspect ratio wing has more mass farther away from the center of rotation.
If you took a long pole, held it lengthwise (like a tight rope walker) and tried to rotate it, it would take more force and move slowly than if you had a short pole and held/rotate it the same way. The shorter pole would move more quickly. It's the same with an airplane.
A high aspect ratio wing is a wing that is long and narrow. A low aspect ratio wing is a short and wide wing:
Aspect Ratio (AR) is defined as:
AR = s^2 / A = s^2 / (s * c) = s / c
AR = wing length / wing width
Gliders and long range aircraft have high aspect ratio wings to take advantage of the efficiency of of the wing at cruise.
Fighters and aerobatic aircraft tend to have low aspect ratio wings to take advantage of the maneuverability.
A great example of aircraft combining the best of both worlds are aircraft with variable geometry wings like the F-11 Aardvark:
And the F-14 Tomcat:
Something to consider: as you go above the speed of L/D max, the efficiency of a wing diminishes rapidly as drag becomes higher at high speeds. Therefore, very high speed (supersonic) aircraft desire a low aspect ratio wing to experience less drag and better efficiency at very high speeds.