In the field of commercial real estate, especially in the United States, a net lease requires the tenant to pay, in addition to rent, some or all of the property expenses that normally would be paid by the property owner (known as the "landlord" or "lessor"). These include expenses such as property taxes, insurance, maintenance, repair, and operations, utilities, and other items. These expenses are often categorized into the "three nets": property taxes, insurance, and maintenance. In US parlance, a lease where all three of these expenses are paid by the tenant is known as a triple net lease, NNN Lease, or triple-N for short and sometimes written NNN.

The term "net lease" is distinguished from the term "gross lease". In a net lease, the property owner receives the rent "net" after the expenses that are to be passed through to tenants are paid. In a gross lease, the tenant pays a gross amount of rent, which the landlord can use to pay expenses or in any other way as the landlord sees fit. Gross leases typically have higher rent charges to recuperate some of these expenses in the rent line, as opposed to doing so through a net arrangement.

The precise items that are to be paid by the tenant are usually specified in a written lease. For properties that are leased by more than one tenant, such as a shopping center, the expenses that are passed on to the tenants are usually pro-rated among the tenants based on the size (square footage) of the area occupied by each tenant. Many variations exist, with options to control any year-to-year variations in fees and such.