Yes, THRESHOLD is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, R 1, E 1, S 1, H 4, O 1, L 1, D 2.

Is it a valid word?

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

the starting point for a new state or experience
the smallest detectable sensation
the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close
the sill of a door; a horizontal piece of wood or stone that forms the bottom of a doorway and offers support when passing through a doorway
a region marking a boundary

Also: room access.