Definitions do different jobs
A definition is not just a sentence that tells you what a word means. In logic, definitions can report ordinary usage, fix a temporary rule, sharpen a vague boundary, support a theoretical explanation, or even smuggle in an evaluative attitude under the guise of neutral clarification. The right definition depends on the job the definition needs to do, and recognizing that job is the first analytic move you should make when you encounter any definition.
That is why the same term may be defined differently in a classroom policy, a legal code, a scientific theory, and an everyday conversation. You should not assume those differences show confusion. Often they show that the context has changed, and the definition has been adapted to serve a new function. A medical researcher defining 'obesity' by body-mass-index thresholds is doing something very different from a philosopher asking what 'obesity' means as a social category, and both are doing something different from a dictionary recording ordinary usage.
The habit of asking 'what is this definition trying to do?' before evaluating whether it succeeds is the single most important analytic habit this lesson teaches. Without it, students routinely judge definitions against the wrong standard, criticizing a stipulative definition for not matching ordinary usage, or dismissing a theoretical definition because it sounds unfamiliar. The function question prevents these category errors.