# line

The graph of *y* = *ax* + *b*, the prototypical linear relationship.

A line is the shortest distance between any two points in Euclidean
space. A line is implicitly a **straight line**. It has
only one dimension, length, may be infinite in extent, and is the shortest
distance between any two points.

Although in common parlance a straight line is not curved, it is a curve in the mathematical sense (i.e., a mapping of an infinite set of points
into a space). Mathematically, a line may be determined by the presence
of any two points in an *n*-dimensional space (where *n* is
two or more). A **line segment** is a piece of a line with
definite endpoints.

In two dimensional Cartesian coordinates, the equation of a line has the
form *y* = *ax* + *b*, where *a* and *b* are constants.