Her necklace had a beautiful cat's eye stone.

'Apple' is a count noun, and you can count it as one, two, etc.

Happiness is a mass noun, you can't count it.

I obtained the natural coat certificate for my dog.

This certificate of value proves the value of the product.

Please remember to bring your travel documents.

I had a hard time finding my birth certificate.

May I show you my proof of qualification?

He is an expert at chess.

A count noun, or 'kasu meishi', represents something that can be counted.