Is this question on mathematical notation on topic? Why the letter q for the line equation y = mx + q? Is it used only in Italian?
There are many mathematicians here (me included), so we may be partial in its favor, but it seems to me that it is very borderline. It is not, strictly speaking, about language, and I find it difficult to formulate a rule that makes it on-topic without being too broad. In addition, since there is [hsm.se], one might argue that it is a better fit there.