Definition
Within a TRACON facility, sectors are the defined sub-areas of the overall airspace, each assigned to a specific controller who is responsible for separating and sequencing the aircraft within that sub-area. As traffic moves through TRACON airspace, it is handed off from one sector controller to the next.
Plain English
A sector is a slice of the airspace that one controller is in charge of. The big block of airspace handled by the radar facility is split into smaller pieces so each controller only has to manage the traffic in their own piece.
Context Anchor
Seen in TRACON and approach-control discussions, especially when describing how radar controllers manage aircraft around busy airports.
Derivation
From Latin 'sector,' meaning 'a cutter' or 'one who cuts,' from 'secare' (to cut). A sector is literally a portion 'cut out' of a larger whole — here, a piece cut out of the TRACON's total airspace.
Why Pilots Care
Each frequency change you get inside TRACON airspace usually means you are crossing into a new sector. Knowing this helps you anticipate handoffs and understand why the controller's workload and instructions can change as you move through the area.
Intuition Check
Do not read sectors as just general areas or compass directions. In this context, sectors are specific airspace responsibility areas assigned to controllers.
Example Sentence 1
Approach split the airspace into several sectors, so we changed frequencies twice before being handed off to the tower.
Example Sentence 2
TRACON divides busy terminal airspace into multiple sectors so each controller can focus on a smaller volume of traffic.