This document discusses various geometry concepts related to parallel and perpendicular lines and planes including: parallel lines never intersect and exist on the same plane, parallel planes never touch; skew lines exist in different planes and do not intersect; a transversal is a line that crosses two parallel lines; corresponding, alternate interior/exterior, and same-side interior angles are defined; the corresponding angle, alternate interior angle, and same-side interior angle theorems state relationships between these angles for parallel lines cut by a transversal; and the transitive property applies to parallel and perpendicular lines and their relationships with a third line.