Line

For other uses, see Line (disambiguation).

Not to be confused with Lime or Lime (color).

A line is the path of one point that is moving. A line is a type of geometric figure. A line has length, but no width. A line is made up of an endless number of points.

Straight and curved lines

This is a line that curves

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 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. It is an example of a curve.

Line segments

A line segment is part of a line. Here are examples of straight line segments:

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Naming lines

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

Sometimes, lines are named with just one symbol. 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.

Related pages

• Linear function
• Point (geometry)
• Plane (mathematics)