Yes, RELAYS is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, L 1, A 1, Y 4, S 1.

Is it a valid word?

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

the act of passing something along from one person or group to another
a crew of workers who relieve another crew
a fresh team to relieve weary draft animals
a race between teams; each member runs or swims part of the distance
electrical device such that current flowing through it in one circuit can switch on and off a current in a second circuit

Also: relay race, electrical relay.