What does 'establishment' mean in real estate industry?
Establishments are business locations (source). The real estate industry does not include construction (under either NAICS or SIC). It’s not really possible to tell what exactly would be included without more detail on the specific industry group you are looking at; it could be anything from realtors’ offices to apartment rental buildings, or both+other types of establishments. A summary of the NAICS groups can be found here.