Plain English Meaning
A government service pilots contact for weather briefings, to file or open a flight plan, and to get help with information about a route. It is staffed by specialists who give advice and information but do not direct traffic.
Full Definition
An air traffic facility that provides pilot briefings, relays clearances between pilots and air traffic control, supports search and rescue, assists pilots in distress, originates Notices to Air Missions (NOTAMs), processes flight plans, and monitors navigational aids. FSS specialists do not separate or sequence ; they are an information and assistance service, not a facility.