Answer: The undefined terms in geometry called undefined because using the three undefined terms (point, line and plane) we can define other terms in geometry.
Explanation:
In geometry, we have three undefined terms: point, line and plane.
An expression in mathematics is said to be undefined if it does not have any meaning but it is used to define other mathematical terms.
Similarly the undefined terms in geometry are words that don't require any formal definition. They create the building blocks for either properly defining or proving theorems and other terms.
Generally we can say that by using the three undefined terms (point, line and plane) we can define other terms in geometry.