Final answer:
A word that has been explicitly given a meaning through definitions in mathematics is known as a defined term.
Step-by-step explanation:
A word that has been defined in the context of mathematics is referred to as a defined term. Defined terms are essential in mathematics because they provide precise meanings to concepts and allow for clear communication and understanding. Unlike undefined terms, which are basic terms that do not have formal definitions but are understood through examples and intuition, defined terms are explicitly given a meaning through definitions. On the other hand, a theorem is a statement that has been proven based on previously established statements, such as axioms and other theorems. An axiom, similar to a postulate, is a statement that is accepted as true without proof and serves as a starting point for further reasoning and arguments.