In the strictest sense, equivocation is the use of different meanings or senses of a word as if they were the same thing.
In a broader sense, equivocation need not be limited to a single word; a phrase or even concept may have different facets or be applied to different instances of the same idea which, although related, are not freely interchangeable. A word used in the same sense may even be referring to a different instances of that sense:
- Person A: I refuse to continue this argument without a mediator.
- Person B: No, I won't allow you to just back out of this. You don't have the right.
- Person A: I don't need your approval; those are my terms, take them or leave them.
- Person B: So what's to negotiate? You've already dictated your terms.
In this case, Person B is equivocating Person A's usage of "terms" meaning terms under which A is willing to continue the discussion, with terms which might be arrived at in that discussion (presumably with the aid of a mediator). (In the real-world example from which this was excerpted and paraphrased, there was substantial discussion between the last two lines, making it less obvious where the equivocation had taken place.)
This might also be called "Confusion of Terms", though I have not been able to find any references to that phrase clearly used in this way. -W.