Which phrase best describes the word definition in an axiomatic system?

The phrase that best describes the word definition in an axiomatic system is:

"Primitive concept"

Here's why:

* Axiomatic systems are built on a foundation of undefined terms called primitives or axioms. These are the basic building blocks that are assumed to be true without needing proof.

* Definitions in axiomatic systems are not used to explain the meaning of the primitive concepts, but rather to define new terms and concepts based on the existing primitives.

* Therefore, definitions in axiomatic systems are derived from the primitive concepts, and their meaning is ultimately grounded in those undefined terms.

For example, in Euclidean geometry, the concepts of "point" and "line" are primitives. We don't define them, but we use them to define other concepts like "angle", "triangle", etc.