Yes, PARAMETER is a Scrabble word!

Letter values in Scrabble US: P 3, A 1, R 1, A 1, M 3, E 1, T 1, E 1, R 1.

Is it a valid word?

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

a constant in the equation of a curve that can be varied to yield a family of similar curves
any factor that defines a system and determines (or limits) its performance
(computer science) a reference or value that is passed to a function, procedure, subroutine, command, or program
a quantity (such as the mean or variance) that characterizes a statistical population and that can be estimated by calculations from sample data

Also: parametric quantity.