A line segment is a straight path between two points that has a definite beginning and end. Think of it like a piece of uncooked spaghetti lying flat on a table: it goes straight from one end to the other, and both ends are right there where you can see them.

In geometry class, you'll draw line segments all the time. If you put your pencil on point A and draw straight to point B without lifting your pencil, you've made a line segment. Mathematicians name line segments by their endpoints, so the segment from point A to point B is called “segment AB” or written as AB with a little bar over the top.

Line segments are different from lines, which go on forever in both directions like railroad tracks stretching to the horizon. They're also different from rays, which have one endpoint but then continue infinitely in one direction, like a beam of light from a flashlight. A line segment is the most practical of the three because you can actually measure it: it has a specific length, whether that's 5 centimeters or 12 inches.

You see line segments everywhere in the real world. The edge of your desk is a line segment. Each side of a stop sign is a line segment. Even the chalk line a baseball umpire draws is technically a line segment, since it starts and stops at specific points.