A line is a long, thin mark that you can draw using a pencil and paper.

In geometry, we mean more specific things by "line". A line must have the following properties:

• They are straight and do not include any curves.
• The have no breadth (thickness).
• They extend infinitely in both directions.

Lines which have two end-points (one at each end) are called line segments. Lines that have one end point, but extend infinitely in the other direction are called rays.