# Line

one-dimensional infinite geometric object

A line is the path of one point moving. A line has length but no width. A line is a type of geometric figure.

A line is made up of an endless number of points.

## Straight and curved lines

A line can be straight or curved. In geometry, the word line means a straight line. A straight line is the shortest distance between two points. A straight line is the line traced by a point moving in a direction that does not change.

A curved line is sometimes called a curve. The edge of a circle is not straight and is an example of a curve.

## Line segments

A line segment is part of a line. Here is an example of a straight line segment:

## Naming lines

Lines can get their names from any two points on the line. For example, if a line contains two distinct points, named $A$  and $B$ , then the line can be called either ${\overleftrightarrow {AB}}$ , or ${\overleftrightarrow {BA}}$ .

Sometimes, lines are also named with just one symbol. In which case, a letter such as $\ell$  might be used.

## Two lines

Two lines can be:

• Parallel: Two lines are parallel if they are on the same plane and they never touch.
• Concurrent: Two lines are concurrent if they touch on one point.
• Coincident: Two lines are coincident if they are made of the same points.
• Perpendicular: Two lines are perpendicular if they make four right angles where they touch.
• Skew: In Euclidean space, two lines are skew if they are not parallel but they never touch.