Final answer:
The imaginary line extending from the leading edge to the trailing edge of a wing is known as the chord line, which is significant in aerodynamics to define a wing's properties.
Step-by-step explanation:
The imaginary line extending from the leading edge to the trailing edge of the wing is called the chord line. In aerodynamics, the chord line is an essential reference in the analysis of a wing's properties. It is used to define the wing's orientation and airfoil sections, which are profiles of the wing's cross-sectional shape. The length of the chord line is simply known as the chord and is key to determining the aerodynamic characteristics such as lift and drag of the wing.