Definition
The position of an aircraft when a navigation station (such as a VOR or NDB) is directly off the wingtip, at approximately a 90-degree angle to the aircraft's track. When abeam a station, the bearing to the station is perpendicular to the aircraft's course.
Plain English
The moment your aircraft is exactly off to the side of the navigation station on the ground, with the station sitting straight out from your wing rather than ahead of you or behind you.
Context Anchor
Used in instrument navigation when judging your position relative to a ground radio navigation station during station passage or while tracking a course.
Derivation
Abeam' comes from the nautical term meaning 'on the beam' — the beam of a ship being its widest point, which runs side-to-side. Something abeam is therefore directly off the side. Aviation borrowed the term unchanged from maritime use.
Why Pilots Care
Pilots use the abeam point to start timing outbound legs in holding patterns and to know when to begin a turn or descent after passing a station off-airport.
Intuition Check
Do not read station as a train or passenger station here. In this context, it means a fixed ground navigation site used by aircraft. Abeam does not mean near the station in any direction. It means off to the side, about 90 degrees from your course or track.
Example Sentence 1
Report abeam the VOR so we can begin timing the outbound leg.
Example Sentence 2
On the approach plate the fix is labeled abeam the VOR, so the crew noted the DME and began descent.