What is the name of line segment an on the circle below

C

Step-by-step explanation:

Let's break down the definitions.

diameter = a line across the circle that crosses the center

radius = a line from the center of the circle to any edge

chord = a line with both endpoints on the edge of the circle

arc = the outside part of the circle

Since this line has both endpoints on the edge of the circle and does not cross the center, the line is a chord.