This is a common vernacular definition regarding low – level offline and online casinos.
Grind Joint – gambling establishment. low level, with disgusting service and most likely unclean the administration practicing fraudulent activities.
It's not always an underground establishment. Even a legally operating casino can be considered a Viper if it does not respect customers and deceives players.
This definition has a bright negative color. It is often used to describe any institutions, even those not related to gambling business.