Parallel lines: Lines in the same plane that never cross or intersect.
Intersecting: Lines in the same plane that meet or cross.
Perpendicular: Lines in the same plane that intersect at a 90 degree angle.
Line Segment: A piece of a line with starting and ending points.
Bisect: To cut in half ("Bi" means "two" and "sect" means "to cut.")
Perpendicular Bisector: A line that divides another segment in half and meets at right (90 degree) angles.
Angle Bisector: A line that divides an angle into two equal parts.