'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.

Abstract nouns, unlike nouns that refer to concrete things, refer to concepts or states that do not have a specific shape or color.

He is learning how to use collective nouns.

He is learning how to use gerunds.

Compound nouns are a very important part of Japanese grammar.