Premises are the buildings and land that belong to a business, organization, or property owner. When a sign says “No skateboarding on the premises,” it means you can't skateboard anywhere on that property: not in the parking lot, not on the sidewalks, not near the buildings. When a store closes for the night, employees might need to leave the premises before the alarm system turns on.

The word emphasizes the whole property as a unit. A school's premises include the entire property: classrooms, playgrounds, cafeteria, gym, and parking areas. If someone is asked to leave the premises, they must exit the entire property, not just move to a different room. In law and contracts, premises is important because it defines exactly what space people are talking about.

Notice that premises is plural even when talking about a single property. You wouldn't say “the premise” when you mean a building and its grounds. That would be confusing, since “premise” (singular) usually means a basic assumption or starting point for an argument.