Yes, TERABYTE is a Scrabble word!

Letter values in Scrabble US: T 1, E 1, R 1, A 1, B 3, Y 4, T 1, E 1.

Is it a valid word?

TERABYTE is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

a unit of information equal to 1000 gigabytes or 10^12 (1,000,000,000,000) bytes
a unit of information equal to 1024 gibibytes or 2^40 (1,099,511,627,776) bytes

Not playable in Scrabble US: TB, TEBIBYTE, TIB.