Yes, BACKGROUND is a Scrabble word!

Letter values in Scrabble US: B 3, A 1, C 3, K 5, G 2, R 1, O 1, U 1, N 1, D 2.

Is it a valid word?

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

a person's social heritage: previous experience or training
the part of a scene (or picture) that lies behind objects in the foreground
information that is essential to understanding a situation or problem
extraneous signals that can be confused with the phenomenon to be observed or measured
relatively unimportant or inconspicuous accompanying situation
the state of the environment in which a situation exists
(computer science) the area of the screen in graphical user interfaces against which icons and windows appear
scenery hung at back of stage

Also: background knowledge, background signal, screen background, play down.