Yes, SPECIFYING is a Scrabble word!

Letter values in Scrabble US: S 1, P 3, E 1, C 3, I 1, F 4, Y 4, I 1, N 1, G 2.

Is it a valid word?

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

specify as a condition or requirement in a contract or agreement; make an express demand or provision in an agreement
decide upon or fix definitely
determine the essential quality of
be specific about
define clearly
design or destine
select something or someone for a specific purpose

Also: pin down, peg down, nail down, narrow down, set apart.

Not playable in Scrabble US: DELIMITATE.