Definition
A method controllers use to describe the direction of traffic relative to the nose of an aircraft, where the position of each hour on a clock face represents a bearing from the aircraft. 12 o'clock is directly ahead, 3 o'clock is directly off the right wing, 6 o'clock is directly behind, and 9 o'clock is directly off the left wing. The reference is always the aircraft's ground track (its actual path over the ground), not its heading.
Plain English
A way of telling a pilot where to look for other traffic by using clock positions. Imagine a clock laid flat over the airplane with 12 at the front; the controller calls out the hour where the traffic is. "Traffic at 2 o'clock" means look forward and slightly to the right.
Context Anchor
Heard in controller traffic advisories, such as when a controller points out nearby aircraft for you to look for.
Derivation
The phrase comes from the face of a traditional 12-hour clock. Aviation uses the clock face as a simple picture of directions around the airplane, with the airplane's nose pointing toward 12.
Why Pilots Care
Enables quick visual acquisition of traffic without converting numbers or headings under time pressure.
Analogy
Imagine your airplane sitting in the middle of a clock face. The nose points to 12, your right wing points to 3, the tail points to 6, and your left wing points to 9.
Intuition Check
This is not about the time of day. In this context, clock numbers tell you direction around your airplane.
Example Sentence 1
ATC called, "Cessna 234, traffic at 10 o'clock, two miles, opposite direction," and the pilot looked forward and to the left to spot the other aircraft.
Example Sentence 2
The pilot scanned the 12-hour clock positions to locate the reported traffic before turning final.