I am looking for a definition of open and dense substack of a Deligne-Mumford stack $\mathcal X$.
I have looked at the one on nlab - dense subtopos, but, as I don't know much about topos theory, I am wondering whether there is a definition which does not use the characterisation of DM-stacks as ringed topoi locally equivalent to the étale spectrum of a commutative ring.
Furthermore, is this notion stable under 2-pullback in the 2-category of stacks?