The phrase arguing semantics doesn't really indicate that the discussion is about something other than meaning, just that the precise nature of that meaning is not terribly important. That's something to keep in mind if you find yourself in an argument with a linguist or a semiotician.

What does don't argue semantics mean?

When someone says an argument has become about "mere semantics" (or whatever), that's usually taken to mean that the nature of the disagreement has shifted from being about concepts to being about words.

What does it mean to say semantics?

"'It's just semantics' is a common retort people use when arguing their point. What they mean is that their argument or opinion is more valid than the other person's. It's a way to be dismissive of language itself as carrier for ideas.