There are two types of tenancy agreements that a lessor/landlord and a tenant can enter into. The first is a fixed- term agreement and second is a periodic tenancy agreement.
A fixed-term tenancy has a definite commencement date and expiry date. A periodic agreement has a commencement date with no expiry date.
Tenancy agreements do not necessarily have to be for a 6 or 12-month term. Sometimes it is best practice to enter into a varied term (i.e. 5, 8 or 10- month tenancy) to avoid the property becoming available over Christmas or other inconvenient time for either the tenant or landlord.