Yes, SALE is a Scrabble word!

Letter values in Scrabble US: S 1, A 1, L 1, E 1.

Is it a valid word?

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

a particular instance of selling
the general activity of selling
an occasion (usually brief) for buying at specially reduced prices
the state of being purchasable; offered or exhibited for selling
an agreement (or contract) in which property is transferred from the seller (vendor) to the buyer (vendee) for a fixed price in money (paid or agreed to be paid by the buyer)

Also: cut-rate sale, sales event, sales agreement.