(i) In line segment two points are connected with a straight line.

A line segment has two end points with a definite length.

(ii) A ray is a part of line with one end point and infinitely extends in one direction. It can show by drawing an arrow at one end of the ray.

(iii) Parallel lines are lines that never cross one another. Parallel lines do not intersect to each other.

(iv) A straight line extends from a point indefinitely in one direction only. It is the set of all points on a line on a given side of a given point of the line.

Notation:

is the half-line.

(v) When three or more points lie on a straight line called collinear points. If the points lie on the same line then the points are called collinear points.

A, B and C the collinear points.

(vi) A plane is a flat surface with no thickness. A plane is two dimensional.