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

This plan is impossible.

Unexpectedly, his face came to mind.

He is always joking around during class.

His irregular lifestyle is having a negative impact on his health.

He likes to take a walk in the park at dusk.

He is receiving countless blessings.

The indefinite article is a basic part of English grammar.

Mr. Shinobu is my best friend.

This area is a no-entry area.