Yes, RESERVATION is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, S 1, E 1, R 1, V 4, A 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

a district that is reserved for particular purpose
a statement that limits or restricts some claim
an unstated doubt that prevents you from accepting something wholeheartedly
the act of reserving (a place or passage) or engaging the services of (a person or group)
the written record or promise of an arrangement by which accommodations are secured in advance
something reserved in advance (as a hotel accommodation or a seat on a plane etc.)
the act of keeping back or setting aside for some future occasion

Also: mental reservation, arriere pensee.