Aspect Ratio

Aspect ratio is a measure of the ratio between the span of the wing to its chord. In most cases the wing chord is not equal along the length of the span which is why aspect ratio is most commonly calculated by dividing the square of the wing span by the reference wing area.

aircraft-aspect-ratio-formula
Definition of Aircraft Aspect Ratio

The effects of aspect ratio on the design of an aircraft wing is discussed in further detail in Part 3 of the Fundamental Aircraft Design Series.