Parallel lines parallel lines are lines in a plane which do not meet; that is, two lines in a plane that do not intersect or touch each other at any point are said to be parallel. By extension, a line and a plane, or two planes, in three-dimensional Euclidean space that do not share a point are said to be parallel. However, two lines in three-dimensional space which do not meet must be in a common plane to be considered parallel; otherwise they are called skew lines. Parallel planes are planes in the same three-dimensional space that never meet.

lnterionr angles https://en.wikipedia.org/wiki/Parallel_(geometry) Any of the four angles formed inside two straight lines when these lines are intersected by a third straight line. An angle formed by two adjacent sides of a polygon and included within the polygon. Compareexterior angle.

3.Exterior angles Interior and exterior angle formulas: The sum of the measures of the interior angles of a polygon with n sides is (n – 2)180. The measure of each interiorangle of an equiangular n-gon is. If you count oneexterior angle at each vertex, the sum of the measures of the exterior angles of a polygon is always 360°.