I'm surprised you feel its meaningless, given its a widely used term.
https://en.wikipedia.org/wiki/Vacant_possession
Vacant possession is a property law concept.
vacant possession refers to a legal obligation to ensure that a property is in a state fit to be occupied at a given point in time. Vacant possession is most commonly known of on the sale and purchase of residential property and many find that, on the purchase of a new home, they do not obtain vacant possession as desired. The concept is also an essential element in the grant and termination of leases and other tenancy agreements. It is a topical issue for lawyers and surveyors along with estate agents and others connected to land and buildings.