What Are Consecutive Angles?

Consecutive angles lie along the transversal

When transversals cross through two parallel lines, they create two identical sets of angles. The angles that would be supplementary (next to each other, in this case) on one side of the transversal are called consecutive.

A set of consecutive angles is always made up of one angle from each set: in the image above, the angles with arcs of the same color are consecutive to each other. Both angles will always be on one side of the transversal, and they'll either both be inside the parallel lines or outside the parallel lines (interior or exterior angles, respectively).

Consecutive angles are always supplementary if the transversal crosses parallel lines.