Yes, INFLECTION is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, F 4, L 1, E 1, C 3, T 1, I 1, O 1, N 1.

Is it a valid word?

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

a change in the form of a word (usually by adding a suffix) to indicate a change in its grammatical function
the patterns of stress and intonation in a language
deviation from a straight or normal course
a manner of speaking in which the loudness or pitch or tone of the voice is modified