Yes, FRONTIERS is a Scrabble word!

Letter values in Scrabble US: F 4, R 1, O 1, N 1, T 1, I 1, E 1, R 1, S 1.

Is it a valid word?

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

a wilderness at the edge of a settled area of a country
an international boundary or the area (often fortified) immediately inside the boundary
an undeveloped field of study; a topic inviting research and development