Yes, SECRETS is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, C 3, R 1, E 1, T 1, S 1.

Is it a valid word?

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

something that should remain hidden from others (especially information that is not to be passed on)
information known only to a special group
something that baffles understanding and cannot be explained

Also: closed book.