Line segment:
A line segment is a part of a line consisting of two points, called end points, and the set of all points between them.
A line segment is identified by naming the two end points and drawing a line over the letters
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Ray:
A ray is a part of a line consisting of a given point, called the end point, and the set of all points on one side of the end point.
A ray is always named by using two points, the first of which must be the end point. The arrow drawn above always points to the right: