This is best shown by way of the following example.
A landlord owns commercial premises and their tenant is leasing the premises for 12 years. In year 6 of the lease, the tenant decides to close their business and no longer wants the commercial premises.
The tenant needs to transfer or assign their lease to another business for the rest of the term of years left on the lease, otherwise, they’ll have to pay the rent for another 6 years. The tenant needs permission to assign the lease and this is given by way of a Licence to assign signed by the landlord, the outgoing tenant and the incoming tenant.
You’ll then need a deed of assignment to actually implement the transfer of the lease.