What does supplementary mean?

The question, most likely, is about supplementary angles. Two angles are called supplementary if a sum of their measures equals to ##180^o## (in degrees) or ##pi## radians.

On a picture below angles ##/_KML## and ##/_KMH## are supplementary. They also happened to be adjacent to better illustrate that their sum equals to ##180^o##, but this is not necessary since supplementary angles can be positioned anywhere.

Here is a more general position of two supplementary angles: