In the Commercial Real estate realm, you often see retail rents quoted in terms of NNN or "triple net". What that means is that the tenant is required to pay, in addition to rent, some or all of the property expenses that would normally be paid by the landlord. In other words, the rent quoted is net of expenses such as taxes, insurance, utilities, capital expenses, maintenance, etc. Why triple then? The most common reimburseable expenses include real estate taxes, insurance, and CAM (common area maintenance). But they could also include additional costs such as administrative fees, marketing fees, trash fees, etc.
So when Mr. Landlord tells you, the rent is $25.00 NNN and the Nets are $4.00, this actually means you would be paying $25.00 per square foot per year and an estimated $4.00 per square foot per year in addition. I highlight estimated because those Nets will ultimately be reconciled at year end by actual costs.
At the end of the day, read your lease carefully and speak to a real estate attorney about your ultimate lease obligations.