Gross leasable area, or GLA, is the amount of space in an a commercial building that can actually be rented by a tenant. In most cases, this includes any basements, mezzanines, or upper floors that a tenant can potentially utilize. Typically GLA is measured from the center of a wall or other partition that separates tenants (such as retail stores in a shopping mall), from the lease line in common areas, and fully takes into account any walls that are not shared with other tenants.
A BPO, or broker price opinion, also known as a BOV, or broker opinion of value, is an estimate provided by a real estate broker to help a potential investor get a better idea of how much they should bid for a property. A BPO/BOV is not held to the same standard as an appraisal, but it is typically much faster and much less expensive.