Angles with the same measure.
An angle that measures 180 degrees (opposite rays).
Two angles whose sum is 90 degrees.
Two angles whose sum is 180 degrees.
Two angles that share a common vertex or side, but have no common interior points. (e.g. an angle bisector)
When the noncommon sides are opposite rays. (e.g. a straight angle with an angle bisector)
When sides form two pairs of opposite rays. (e.g. a plus sign)
Closed plane figure, has three or more sides, can't be bowtie, can't be curved, can't be open.
A polygon that doesn't contain a side of it in the interior of the shape.
A polygon that has a side in the interior of it.
If all of the sides are congruent.
If all of the angles are congruent.
Both equiangular and equiregular.