Semantic means “about what words mean” — not about spelling, not about how a sentence is built, but about the meaning sitting in the words. A semantic question is: does this word point to the same idea as that one? Linguists use it all the time. Computer people use it too, when they talk about a semantic error: the code is legal as grammar, but it does not mean what you wanted. The everyday cousin is simply “the meaning of the word”; semantic is the slightly school-and-university way of pointing at that same area. People also stretch it: a semantic argument is one where you agree on the facts but you are fighting over what a word covers.