A Lessor is the person or entity who grants a lease to another party.
In oil and gas, it’s the mineral owner (often the “landowner”) who is the Lessor, that grants a lease to another party, the Lessee. The Lessee is usually either a broker, often known as a landman, or an operating oil and gas company.
Again, within the context of upstream oil and gas, the Lessee makes a one-time payment, the lease bonus, based on the amount of net mineral acres, plus the commitment to paying an ongoing royalty payment, based on the value of hydrocarbon production, IF any is found and produced.