Definition of "substack"

In particular, we give necessary and sufficient conditions for the existence of Poincar\'e bundles over the universal curve of an open substack of the rigidification, generalizing a result of Mestrano-Ramanan..

2016, Roberto Fringuelli, “The Picard group of the universal moduli space of vector bundles over M ¯ g {\displaystyle {\bar {\mathcal {M}}}_{g}} ”, in arXiv‎