A geometric line segment is a straight path of points(that is a line) that has two end points (that is a beginning and an end). A 10 yard line on a football field is a line segment because it has two endpoints which is at the beginning of the 10 yard and at the end of the 10 yard.
A scientist's line of vision as he looks into space with a telescope is not a line segment because it extends forever (has no end).
A line of 15 dancers on stage is not a line segment, A light shone into the darkness is not a line segment because it continues forever and also, the hands of a clock is also not a line segment.
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