A Noun is a word used as the name of a person, place or thing.
Look at the following sentence:
Asoka was a wise king.
The noun Asoka refers to a particular king, but the noun king might be applied to any other king as well as to Asoka. We call Asoka a Proper Noun, and king a Common Noun.
Similarly:
The word girl is a Common Noun, because it is a name common to all girls, while Sita is a Proper Noun because it is the name of a particular girl.
Def. - A Common Noun is a name given in common to every person or thing of the same
class or kind.
Def. - A Proper Noun is the name of some particular person or place,
Note 1 - Proper Nouns are always written with a capital letter at the beginning.
Note 2 - Proper Nouns are sometimes used as Common Nouns; as,
1. He was the Lukman (= the wisest man) of his age.
2. Kalidas is often called the Shakespeare (= the greatest dramatist) of India.
Common Nouns include what are called Collective Nouns and Abstract Nouns
A Collective Noun is the name of a number (or collection) of persons or things taken together and spoken of as one whole; as,
Crowd, mob, team, flock, herd, army, fleet, jury, family, nation, parliament, committee.
An Abstract Noun is usually the name of a quality, action, or state considered apart from the object to which it belongs; as.
Another classification of nouns is whether they are 'countable' or 'uncountable'.
Countable nouns (or countables) are the names of objects, people, etc. that we can count, e.g., book, pen, apple, boy, sister, doctor, horse.
Uncountable nouns (or uncountables) are the names of things which we cannot count,
e.g., milk, oil, sugar, gold, honesty. They mainly denote substances and abstract things.
Countable nouns have plural forms while uncountable nouns do not. For example, we say 'books' but we cannot say 'milks'.