a plane figure bounded by two radii and the included arc of a circle
"When measuring the area for our new garden, we calculated that each triangular sector of the circular pond would hold exactly ten goldfish."
the minimum track length that can be assigned to store information; unless otherwise specified a sector of data consists of 512 bytes
"The system failed because the corrupted file was too large to fit within a single disk sector."
a portion of a military position
"The commander ordered reinforcements to hold the northern sector of our defensive line against the advancing troops."
measuring instrument consisting of two graduated arms hinged at one end
"The surveyor carefully aligned the sector's two graduated arms to calculate the distance across the river without needing a modern laser rangefinder."
section
"The new marketing team was assigned to a different sector of the store where fewer customers were browsing."
In plain English: A sector is a specific part of a larger group, like a particular industry within the economy or a slice of a circle.
"The government announced new funding plans for the education sector."
The word comes directly from Latin sector, meaning one who cuts or divides. It entered English with the sense of a wedge-shaped portion created by such division.