What is a line ? Definition and examples

In geometry, a line is a set of points that extends in two opposite directions without end.

A straight two-headed arrow is used to represent a line as shown below.

A line is endless in two directions. In other words, it extends indefinitely to the left and to the right.

It is not possible to draw a line on paper because a line is endless. That is why what you see above is a representation of a line.