An undefined term in geometry means that such terms
cannot be explained properly. The examples of undefined terms in geometry are
point, line, and plane. A point is a dimensionless term, which has no length or
width or thickness. Similarly a line or a plane also has no width. A line can
be extended in two directions, while a plane can be extended in all directions.
On the other hand undefined terms combines in a meaningful
way, i.e. when a line crosses another lines, it forms an angle. Thus angle is a
defined term in geometry.
