A Venue is a restaurant, coffee shop, bar, country club. Basically any entity that uses NX Restaurant in their business, is a Venue. Nearly all configuration settings within NX are associated to a Venue. A Venue has Orders, Menu Items, Menu Categories, Sales Categories, Taxes, and many many many more properties.
Venues are grouped under a Tenant and every Venue will be associated with a Tenant even if there is only one Venue.