What is the difference between a net lease, a net net lease and a triple net (nnn) lease?

Double net NN  means that the tenant pays for everything except structural repair.

Triple net NNN means that the tenant is responsible for generally everything including structural repair, BUT every lease is different, it is best to actually see copy of any lease very early in any negotiation process. Many triple net leases hold the landlord still responsible for roof repairs. It is ALWAYS a matter of negotiation between the parties.

 

In residential leasing you deal with people, but in commercial you deal more with contracts and corporations.

 

In addition to NN and the NNN leases,  there is such thing as a Bond Type Lease which basically means that the tenant will pay on the lease no matter what even if the building burns down or other disaster happens.

The advantage of a bond type lease is that the landlord can take that Bond Type Lease and actually securitize it and get money for it, provided of course that the tenant is of investment quality.
Always get complete financials on the tenant or you are wasting your time and be sure it's not some shell company that is a subsidiary of some large company that sounds good, remember, the lease is only as good as the company behind it.