Yes, DESCRIPTOR is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, S 1, C 3, R 1, I 1, P 3, T 1, O 1, R 1.

Is it a valid word?

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

the phonological or orthographic sound or appearance of a word that can be used to describe or identify something
a piece of stored information that is used to identify an item in an information storage and retrieval system

Also: word form.