Short for metropolitan statistical area/rural service area, cellular service areas used by the FCC to license cellular telephone service. There are 306 MSAs and 428 RSAs. Every county in the United States is assigned to one of these markets.
MSAs -- originally used by the US government for grouping census data -- include cities of at least 50,000 people, or urbanized areas of at least 100,000 people and the counties that include these areas.
RSAs include all areas not part of MSAs. These are often rural areas.
In order for a carrier to provide service to specific MSAs and RSAs, it must have a FCC license. If the carrier did receive the license at the time of auction, then it must try to buy it from the successful bidder or create a deal with the rightful owner that allows it to serve that particular area. Multiple licenses are given out per MSA/RSA, and each carrier must transmit over its assigned frequency.
If a carrier can't build a system to serve a certain percentage of the licensed area by a specified deadline date, then it must return the license to the FCC.