Collinear points are points that belong to the same line. If three distinct points are collinear, then one of the points is between the other two. 4. Important subsets of lines are segments, half-lines and rays. A line segment consists of two points and all collinear points between them. Intersecting lines are two lines with exactly one point in common.
Concurrent lines are lines that contain a single common point.
Parallel lines are lines with no points in common. A unique line is determined by two distinct points. A unique plane is determined by three non-collinear points. This axiom can be used to prove that any of the following conditions also generates a unique plane. If the intersection of two distinct planes is not empty, then the intersection is a line.