Wiktionary
n. (label en set phrase) A linguistic or conceptual distinction which is of no practical importance or which has no effect on meaning; a perceived difference where there is no actual difference.
Wikipedia
A distinction without a difference is a type of logical fallacy where an author or speaker attempts to describe a distinction between two things although no difference exists. It is particularly used when a word or phrase has connotations associated with it that one party to an argument prefers to avoid.
Usage examples of "distinction without a difference".
Avarice presently treated this with ridicule, called it a distinction without a difference, and absolutely insisted that when once all pretensions of honour and virtue were given up in any one instance, that there was no precedent for resorting to them upon a second occasion.
Descartes' methodical doubt is ultimately a distinction without a difference, since it has no pragmatic consequences whatsoever.