A line segment is a finite portion of an infinite line. Line segments are ordinarily drawn with a dot on each end and a line in between. The dots are typically labeled A and B. The line segment can be written as AB with a straight line above the letters.
In geometry, a ray is a half-infinite line. That is, it extends infinitely in one direction, but is bounded in the other direction. Rays are typically written as straight lines with an arrow on one end and a dot on the other. The dot and arrow are usually labeled A and B, and the ray can be written as AB with a straight line over the letters, where the straight line has an arrow at one end.
Given two intersecting lines, line segments or rays, the angle between them is defined as the amount of rotation that would be needed to make the lines overlap exactly. Angles can be measured in degrees, minutes and seconds or in radians. There are 360 degrees in a circle, 60 minutes in a degree and 60 seconds in a minute. There are 2*pi radians in a circle (pi = approximately 3.14 and is the ratio of the circumference of a circle to its diameter).
There is an angle between any two rays or line segments that intersect. Rays and line segments are both portions of lines, which are infinite in both directions.