A point is used for marking position; it has neither length, breadth, nor thickness.

A line has length only; it is produced by the motion of a point.

A straight line or right line is one that has the same direction throughout. It is the shortest distance between two points.

A curved line is one that is constantly changing in direction. It is sometimes called a curve.

A broken line is one made up of several straight lines.

Parallel lines are lines which lie in the same plane and are equally distant from each other at all points.

A horizontal line is one having the direction of a line drawn upon the surface of water that is at rest. It is a line parallel to the horizon.

A vertical line is one that lies in the direction of a thread suspended from its upper end and having a weight at the lower end. It is a line that is perpendicular to a horizontal plane.

An oblique line is one that is neither vertical nor horizontal.

In Mechanical Drawing, lines drawn along the edge of the T-square, when the head of the T-square is resting against the left-hand edge of the board, are called horizontal lines. Those drawn at right angles or perpendicular to the edge of the T-square are called vertical lines.

If two lines cut each other, they are called intersecting lines, and the point at which they cross is called the point of intersection.