Gross Floor Area (GFA) is a metric used within the real estate industry to indicate the total amount of space available within a building development including walls, corridors and columns. In the context of REITs and real estate investments, a more telling indicator would be Gross Leasable Area (GLA) which indicates the total amount of floor space that is generating operating income for the building.
In properties with a single tenant such as hotels and hospitals, Gross Floor Area is effectively taken to be the Gross Leasable Area.