Yes, STOCKS is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, O 1, C 3, K 5, S 1.

Is it a valid word?

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

a frame that supports a boat while it is under construction
a frame for constraining an animal while it is receiving veterinary attention or while being shod
a former instrument of punishment consisting of a heavy timber frame with holes in which the feet (and sometimes the hands) of an offender could be locked
the capital raised by a corporation through the issue of shares entitling holders to an ownership interest (equity)
the merchandise that a shop has on hand
the handle of a handgun or the butt end of a rifle or shotgun or part of the support of a machine gun or artillery gun
a certificate documenting the shareholder's ownership in the corporation
a supply of something available for future use
the descendants of one individual
a special variety of domesticated animals within a species
liquid in which meat and vegetables are simmered; used as a basis for e.g. soups or sauces
the reputation and popularity a person has
persistent thickened stem of a herbaceous perennial plant
a plant or stem onto which a graft is made; especially a plant grown specifically to provide the root part of grafted plants
any of several Old World plants cultivated for their brightly colored flowers
any of various ornamental flowering plants of the genus Malcolmia
lumber used in the construction of something
the handle end of some implements or tools
an ornamental white cravat
any animals kept for use or profit

Also: stock certificate, line of descent, blood line, malcolm stock, farm animal, buy in, stock up.