Is a cell or organ that secretes substances for use elsewhere in the body?

The answer is a Gland.

It is a cell or organ that secretes substances for use elsewhere in the body, or for elimination as waste. Secretion being a product of gland if it's useful to the body and an excretion being a product of the gland if it's a waste product. Glands may be exocrine or endocrine; endocrine glands lose contact with surface; have no ducts; secretes products directly into the blood due to having a high density of blood capillaries while exocrine glands secretes to the body surface or lumen; and maintain contact with surface via a duct.