A lessor is a person or organization that owns an asset, such as real estate, and a lessee is a person or organization that makes installment payments to use the asset. In real estate rentals, the lessor is the landlord and the lessee is the renter.
A lease relationship can also exist for non-physical property such as trademarks or brand names. An example is restaurant chains such as Wendy's that allow franchises to use the name in exchange for a franchise fee.
It's important to have a contract that stipulates the agreements and rights of the lessor and lessee as it aids in resolving any disputes that might arise.