It is one method by which expenses are recovered by a landlord from a tenant. NNN is short for "net net net" and is used interchangably with the phrase "triple net."
Terms like NNN or "triple net" don't mean the same thing to every real estate professional so only a lease can give you a definitive answer. To most however, this means that on top of your monthly rental payment, you as tenant are going to be responsible for paying your pro rata share of all operating expenses, including common area maintenance, common utilities, real estate taxes, and insurance.
Some expenses like management fees and maintenance of the roof and structure are passed through in some "net leases" and not in others. Again, the lease governs.
Christopher B. Kubler, CCIM
Feb 21, 2009