A single net lease (N) is a lease in which the tenant pays property taxes in addition to rent, while the landlord covers insurance and maintenance.
Under a single net lease the tenant pays the property tax bill and the landlord covers insurance and maintenance, so the landlord retains a good deal of responsibility and cost. It is less common than NN or NNN leases. Investors typically need to model the landlord's expenses carefully, since NOI is lower than the rent. Compare an N lease to a NNN lease using the real after-expense yield rather than the headline rent.