Definition
Air traffic control services provided by Air Route Traffic Control Centers (ARTCCs) to aircraft operating on IFR flight plans, generally during the en route phase of flight between departure and arrival terminal areas. These services include separation, traffic advisories, weather information, and route or altitude clearances within controlled airspace.
Plain English
The air traffic control help you get from a Center while flying the long middle part of an IFR trip — the cruise portion between leaving your departure airport's local controllers and reaching your destination's local controllers.
Context Anchor
You will see this term in FAA material about who provides air traffic control during the cruise or cross-country portion of a flight.
Derivation
En route' comes from French, literally 'on the way.' It refers to the part of the flight that is on the way to the destination — after departure, before arrival. That matches what these services cover: the middle, traveling portion of the flight.
Why Pilots Care
These services give pilots traffic separation, route clearances, and advisories during the main part of the flight.
Intuition Check
Do not read “en route” as simply “any time the airplane is flying.” Here it means the portion of flight between the departure airport area and the arrival airport area, usually handled by en route controllers.
Example Sentence 1
After departure, the controller handed us off to Center for en route air traffic control services as we climbed to our cruise altitude.
Example Sentence 2
En route air traffic control services provided vectors around a line of thunderstorms.