The same as an everywhere-dense set. More generally, a set is called dense in an open set of a space if is contained in the closure of or, which is the same, if is everywhere dense in the subspace . If is not dense in any non-empty open set , it is a nowhere-dense set in .
Dense set. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Dense_set&oldid=16528