Two angles are called complementary is they add up to 90o. E.g. two acute angles in a right triangle are complementary.
Two angles, the sum of whose measures is ninety degrees. Concept attainment: The process of creating categories by grouping similar objects and ideas…and by finding those attributes that are absolutely essential to the meaning and disregarding those that are not. The adult's role in the child's concept attainment process is to provide an enriched, idea-filled environment so that many examples of many concepts are encountered, and information and feedback regarding the accuracy of the concept definitions are given.
Two angles that add to give 90°, such as the two non-right angles in a right triangle, or the two angles on either side of a line that bisects a right angle. In the image to the right, lines AP and BP create a right angle. CP bisects this right angle. Angles and 2 are complementary, since they add to give 90°. See this link to Math League for more information on complementary angles.