Oxford English Dictionary [< Middle English, < Anglo-Norman and Old French definer to end, terminate, determine]
3. Logic, etc. The action of defining, or stating exactly what a thing is, or what a word means.4. a. A precise statement of the essential nature of a thing; a statement or form of words by which anything is defined.
5. a. The action of making definite; the condition of being made, or of being definite, in visual form or outline; distinctness; spec. the defining power of a lens or optical instrument, i.e. its capacity to render an object or image distinct to the eye.
Wiktionary: 1. A definition that is chosen for an occasion and may not fully conform with established or authoritative definitions.
2. A definition being developed; a tentative definition that can be tailored to create an authoritative definition.
Simplicable Business Guide: A working definition is an explanation of a term that is used for a particular purpose. It is common for terms to have multiple definitions or for definitions to be contentious.
Working definitions serve as a practical reference in the context of a program, project, decision making process or problem solving initiative. The following are illustrative examples.
Consensus: Working definitions are useful for building consensus. It is often difficult to get people to agree on definitions. Working definitions need not be polished and are easier for groups to develop. . . .
Problem Solving: Working definitions can be used to simplify problem solving. For example, a data center support team may clearly define terms such as "hot spot" or "data breach" so that everyone is speaking the same language when working on an incident.
Communication: Working definitions can be developed by organizations and teams as part of their culture to improve communication. For example, a human resources team defines terms such as "professional conduct" and "professional attire" that are commonly used in policy and internal communications. [And thus a "working definition" can change as conditions or personalities evolve.]