Definition 1 of 2
Definition
A defined portion of airspace assigned to a specific air traffic controller for the separation and control of aircraft within that volume. Sectors are bounded laterally and vertically and together make up the larger airspace managed by an Air Route Traffic Control Center (ARTCC) or terminal facility.
Plain English
A slice of the sky that one controller is responsible for. Each controller works their own slice, and aircraft are handed off from one slice to the next as they fly along.
Context Anchor
Pilots most often hear this in air traffic control discussions, especially when a flight is passed from one controller or frequency to another.
Derivation
From the Latin 'sector', meaning 'a cutter' or 'one who cuts', from 'secare' (to cut). In geometry, a sector is a slice cut from a circle. The aviation use carries the same idea: a slice cut out of a larger volume of airspace.
Why Pilots Care
Each frequency change in cruise usually means you are crossing into a new sector. Knowing this helps you anticipate handoffs, understand why workload and service quality can vary along a route, and recognize why the same controller cannot follow you the whole way.
Intuition Check
Sector does not just mean any vague area. In aviation, it usually means a specifically defined part of airspace or an operating area used for control or planning.
Example Sentence 1
After the handoff, the pilot checked in with the next sector and was given a direct routing.
Example Sentence 2
During peak traffic, the supervisor split the busy sector into two smaller ones to keep workload manageable.