Yes, JAIL is a Scrabble word!

Letter values in Scrabble US: J 8, A 1, I 1, L 1.

Is it a valid word?

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

a correctional institution used to detain persons who are in the lawful custody of the government (either accused persons awaiting trial or convicted persons serving a sentence)

Also: put behind bars, put away.