A mass noun refers to a noun that cannot be counted.

He spread the sheets on the bed.

He took out a thousand yen bill from his wallet.

The new edition of this book has been released.

I cast a ballot for the election.

He is painting a picture using a brush.

He lay down on the floor because he was tired.

Fujisan is my best friend.

Hearing the news of his death, I was deeply saddened.

My new kettle is very convenient.