Definition: Two angles that are adjacent
(share a leg) and supplementary (add up to 180°)

Try this Drag the orange dot at M.

In the figure above, the two angles ∠JKM and
∠LKM form a linear pair. They are
supplementary because they always add to 180°
and because they are
adjacent,
the two non-common legs form a straight line segment JKL.