Definition
FLIGHT INFORMATION SERVICE-BROADCAST (FIS-B)
A ground broadcast service provided through the ADS-B Broadcast Services network over the UAT data link that operates on 978 MHz. The FIS-B system provides pilots and flight crews of properly equipped aircraft with a cockpit display of certain aviation weather and aeronautical information.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).