A commercial sublet naturally refers to any sublease agreement involving a commercial space. A sublease differs slightly from a normal direct lease. With a direct lease, the tenant signs a lease agreement directly with the landlord of the space. Then, that tenant pays the landlord each month or however the lease agreement is set up. It is a fairly standard and simple agreement. 

A sublease situation occurs when the tenant (usually with permission from the landlord, but not always) leases out either the entire space or a portion of it to another individual/company. A tenant might choose to do this if they are locked into a lease but are not using the property, or if they want to maintain the lease and use the property at a later date but have no current use for it.

In the sublease agreement, the sublessee pays rent to the sublessor, who in turn pays rent to the landlord (or master lessor). This type of situation might prove beneficial to both the sublessee (looking for a cheap property without a long-term commitment) as well as the sublessor (looking to fill a vacant space that they are locked into a lease for).