A vernissage is an invitation-only or private preview of an art exhibition before it opens for public viewing. It's used as a marketing tool to promote an exhibition, to introduce the artist(s) and their work to important figures in the art establishment, art collectors, and sometimes celebrity guests. Plus journalists in the hope to get some media coverage (preferably favorable, but any publicity is better than none).
The term comes from the French vernissage, which literally means "varnishing", and the tradition in centuries past for artists to use the day before an exhibition opened to put finish touches to their paintings and/or varnish them, once they had been hung.
