What is the difference between a defined and an undefined term in Geometry?

Question

hba · Answer

The difference between defined and undefined terms is that the defined terms can be combined with each other and with undefined terms to define still more terms.

These are undefined terms:
1.plane
2.point
3.line

These are defined terms:
1.ray
2.union of sets
3.space
4.subset
5.set
6.proper subset
7.opposite rays
8.postulate
9.betweenness of points
10.bisector of a segment
11.midpoint of a segment
12.line segment
13.lenght of a segment
14.collinear points
15.complement of a set
16.coplanar points
17.disjoint sets
18.element
19.empy set
20.finite set
21.geometry
22.infinite set
23.intersection of sets