Yes, WINDOW is a Scrabble word!

Letter values in Scrabble US: W 4, I 1, N 1, D 2, O 1, W 4.

Is it a valid word?

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

a framework of wood or metal that contains a glass windowpane and is built into a wall or roof to admit light or air
a transparent opening in a vehicle that allow vision out of the sides or back; usually is capable of being opened
a transparent panel (as of an envelope) inserted in an otherwise opaque material
an opening that resembles a window in appearance or function
the time period that is considered best for starting or finishing something
a pane of glass in a window
an opening in a wall or screen that admits light and air and through which customers can be served
(computer science) a rectangular part of a computer screen that contains a display different from the rest of the screen