The supplement of an angle is another angle that, when added to the original angle, results in a sum of 180 degrees. In other words, if angle A measures x degrees, then its supplement angle B measures (180 - x) degrees. For example, if angle A measures 60 degrees, then its supplement angle B measures (180 - 60) = 120 degrees. Supplementary angles are important in geometry and trigonometry, and they have several properties, such as forming a straight line and having the letter "S" in their abbreviation.