complementary
two angles whose measures add to 90
supplementary
two angles whose measures add to 180
perpendicular lines
two lines that meet to form a right angle
parallel lines
two coplanar lines that do not intersect
adjacent angles
two angles that share a side and vertex
vertical angles
opposite angles (equal in measure)
right angle
an angle with measure 90 degrees
acute angle
an angle with measure less than 90 degrees
obtuse angle
an angle with measure more than 90 degrees but less than 180 degrees
angle bisector
a segment, ray, or line that divides an angle into two smaller, equal angles
straight angle
an angle with measure 180 degrees
linear pair
two angles that are both adjacent and supplementary