Yes, MERIDIANS is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, R 1, I 1, D 2, I 1, A 1, N 1, S 1.

Is it a valid word?

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

the highest level or degree attainable; the highest stage of development
a town in eastern Mississippi
an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator

Also: line of longitude.