What Are Lines?

Lines are defined by points and go forever

Lines are pretty much what you think of when you hear someone say "line." Lines pass through two points in space, and are always straight in geometry. Lines (as opposed to line segments or rays) go forever in both directions—they have no end.

Just like points, lines aren't really shapes, so they don't have any area. While points are "infinitely tiny" (you could say "zero-dimensional"), lines are "infinitely thin" (they are "one-dimensional").

In geometry, lines can be named using the points that they pass through. In the picture above, AD and CB are both lines.

Depending on where they are in a plane or relative to other lines, lines can have special names or special relationships with other figures.