Yes, CONTEXT is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, T 1, E 1, X 8, T 1.

Is it a valid word?

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

discourse that surrounds a language unit and helps to determine its interpretation
the set of facts or circumstances that surround a situation or event

Also: linguistic context, context of use.