Yes, SECTOR is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, C 3, T 1, O 1, R 1.

Is it a valid word?

SECTOR is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a plane figure bounded by two radii and the included arc of a circle
a social group that forms part of the society or the economy
a particular aspect of life or activity
the minimum track length that can be assigned to store information; unless otherwise specified a sector of data consists of 512 bytes
a portion of a military position
measuring instrument consisting of two graduated arms hinged at one end