JB and Joyce - Without "seeing what you're seeing" I can't answer with 100% certainly. However, with that said, I would think it would mean the standard "not applicable". If you were looking at it here on Trulia it could mean that when the data was transferred from the source (Trulia is populated from a variety of different sources) there might not have been something in the source field and the destination added the NA. If you can tell me which listing you're looking at I will be more than happy to try to assist.
Regardless, best wishes with your home search!
Cyndi Daves, Associate Broker
Coldwell Banker High Country Realty