Line (actually a straight line), together with point, is a basic concept of elementary geometry. The idea of line is an abstraction that distills our intuition that a straight line is the shortest way between two points. However, we distinguish between a line and a line segment. A line segment includes theendpoints, i.e. the points that it joins. The line through the two points continues beyond these points indefinitely.
The absence of the endpoints is often hinted to by drawing arrows: