When someone rents a place from the main renter, and then rents it to someone else.
Subtenancy can make people think of complicated renting situations or legal issues.
Examples:
He has a subtenancy for his apartment.
The subtenancy agreement is important.
The subtenancy is a way to rent a place.
The subtenancy is like a renting sandwich!
In the big building, there are many subtenancies.
She has a subtenancy for her room and rents it to her friend.