Yes, MAPPINGS is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, P 3, P 3, I 1, N 1, G 2, S 1.

Is it a valid word?

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

(mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)
(genetics) the process of locating genes on a chromosome

Also: mathematical function, single-valued function, chromosome mapping.