In a Gross Commercial Lease, the tenant pays the landlord a fixed monthly fee for using the space. It is up to the landlord to cover all the operating expenses of the building (liability insurance, property taxes, etc.). While a gross lease may be more expensive than a net lease initially, it can protect the tenant should operating costs increase down the road. It's also generally a simpler lease, because it does not require the allocation of operating costs among the tenants and landlord.
Some of the most important things about a gross lease is determining exactly how the landlord is calculating the rent, which often means getting into the details of how the leased space is measured.