Yes, PUNCTUATION is a Scrabble word!

Letter values in Scrabble US: P 3, U 1, N 1, C 3, T 1, U 1, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

something that makes repeated and regular interruptions or divisions
the marks used to clarify meaning by indicating separation of words into sentences and clauses and phrases
the use of certain marks to clarify meaning of written material by grouping words grammatically into sentences and clauses and phrases

Also: punctuation mark.