Leases are binding contracts between landlords and tenants. Maryland law imposes certain conditions on that contract but otherwise landlords and tenants are free to negotiate their own agreement.
Holding Over is when a tenant continues to live in a premises after the lease has expired. When a landlord consents to a holdover tenant remaining on the premises, a new monthly or weekly tenancy is created.
This articles lists the requirements for terminating or modifying a tenancy. It also covers what happens if a tenant or landlord dies.