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

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

This apple is a countable noun.

A noun is one of the main elements of a sentence.

He is receiving countless blessings.

An uncountable set refers to a set whose elements cannot be counted.

He is learning how to use gerunds.

A common noun refers to a noun that does not point to a specific person or thing.

A proper noun is a noun that refers to a specific person, place, or thing.

What is his real name?