what does nnn actualy stand for?

"NNN" stands for "Net-Net-Net", also referred to as a Triple Net Lease. In referenced to Investment Property, A NNN Lease is a net lease, where the property in which the Tenant is Leasing is responsible for paying the 1. Property Tax, 2. Insurance, 3. and the Maintenance.
These are the three major expenses associated with leasing or owning commercial real estate.
There are also NN Leases and Gross leases, where the owner will pay part of the cost or include
it into the lease. For an owner of a commercial property a NNN Lease is the preferred way of handling the expenses that are associated with the property..

The rent the landlord receives from the tenant is in effect net of expenses.

NNN stands for Triple Net. With this type of lease a tenant will pay for rent and three additional costs associated to the property. (1) the proportional property taxes, (2) the proportional property insurance and (3) proportional common area maintenance charges.
On the other end of the spectrum, some property owners/mangers offer Gross Leases which typically include all of these costs (and sometimes more, like utilities). Any variation between a Triple Net lease and a Gross lease is called a Modified Gross lease.
The rent should reflect the type of lease. For example, the rent charged in a Gross lease should be higher than the rent charged in a NNN lease (for a comparable space, in the same market) since the Gross lease offers more.
*Submitted by: Chuck Maloy, Coldwell Banker Commercial Pinnacle, Rochester, NY

NNN stands for triple net. It means that the tenants pay their prorated portion of taxes, insurance, and maintenance (also referred to as Common area maintenance- CAM). The ratio and what is included in the NNN needs to be spelled out in the lease

For Commercial & Industrial Real Estate, NNN:
N: Property Tax
N: Insurance
N: Additional Landlord Operating Expense CAM's - Common Area Maintenance fees passed on to Tenant