Plain English Meaning
It is the rulebook, agreed between U.S. and European aviation authorities, that says how aircraft and air traffic control computers must talk to each other digitally so that everyone's equipment works together properly.
Full Definition
A jointly published technical standard from RTCA (a U.S. aviation standards organization) and EUROCAE (its European counterpart) that defines the requirements aircraft and ground systems must meet to exchange digital messages over the Aeronautical Telecommunication Network (ATN) at its first operational baseline. ATN Baseline 1 covers the initial set of controller-pilot data link communications (CPDLC) and related air traffic services, ensuring that equipment from different manufacturers and different countries can communicate reliably with each other.
Context Anchor
Seen in instrument procedures and discussions where , , and certified equipment standards are being described.