Definition:Line/Straight Line Segment

Definition
A straight line segment is a line segment which is straight.


 * A straight line segment can be drawn joining any two points.

(: Postulates: Euclid's Second Postulate)

Thus a definition for straight line which is frequently encountered is:
 * A straight line is the shortest distance between two points.

This is all very well but it assumes that the line in question terminates at two particular endpoints.

Also known as
Some sources take straightness for granted, and refer to such as just a line segment.