\begin{definition}[Definition:Line/Straight Line Segment]
A '''straight line segment''' is a line segment which is straight.
{{EuclidSaid}}
:''A straight line segment can be drawn joining any two points.''
({{BookLink|The Elements|Euclid}}: 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.
\end{definition}