Geometry - Lines
Parallel lines - are lines in the same plane that never cross or intersect
Intersecting - lines in the same plane that meet or cross eg. X L T <--- these letters cross or intersect
Perpendicular - lines in the same plane that insect at 90 degree angles L T <--- These letters have perpendicular angles
Line Segments - piece of a line with starting and end points eg. a__________b
These are some definitions for you to know about basic geometry.