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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

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 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 [math]A[/math] and [math]B[/math], then the line can be called either [math]\overleftrightarrow{AB}[/math], or [math]\overleftrightarrow{BA}[/math].

Sometimes, lines are also named with just one symbol. In which case, a letter such as [math]\ell[/math] might be used.[1][2][3]

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


  1. "Compendium of Mathematical Symbols" (in en-US). 2020-03-01. 
  2. Weisstein, Eric W.. "Line" (in en).,wiggles%22%20anywhere%20along%20its%20length.. 
  3. "An introduction to geometry (Geometry, Points, Lines, Planes and Angles)" (in en).,-lines,-planes-and-angles/an-introduction-to-geometry.