On the contrary, it's an axiomatization, and thus only describes the relation between them. If by "what one means by them" you mean a definition, then you'll need a construction for that. Of course, for the most part, the relation between them is what we mean by them; but Hilbert's formalism doesn't seem to be a good way to address such statements as the one that started this, "a point is a line segment of zero length".