Is the word park a noun?

No, the Word 'park' is a singular, common, concrete noun, a Word for an open public area with grass and trees, often with sports fields or places for children to play; an open public area with grass and trees, often with sports fields or places for children to play.

A collective noun is a Word used to group people or things taken together as one whole in a descriptive way, for example a crew of workers, a pride of lions, a bouquet of flowers, etc.