Yes, BROADBAND is a Scrabble word!

Letter values in Scrabble US: B 3, R 1, O 1, A 1, D 2, B 3, A 1, N 1, D 2.

Is it a valid word?

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

of or relating to or being a communications network in which the bandwidth can be divided and shared by multiple simultaneous signals (as for voice or data or video)
responding to or operating at a wide band of frequencies