What is the Meaning & Definition of noun

The word noun notes various applications.

Something that has a real, independent and individual existence

When you want to give account presenting something real, independent and individual existence is said to be substantive.

Importance of someone or something

And also, if the intention is to refer to the essentiality or immense importance of someone or something the noun Word is used to refer to it. For example, "new findings from the research were nouns to advance it and approaching the guilty."

Grammar: class of words that are the subject of a sentence and identify people, things, animals

Meanwhile, the most widespread use which has the word occurs at the behest of the scope of the grammar and refers to that kind of words that can be the subject within a sentence, which also allows identify or name a person, a thing, one animal, among others.
Then, the noun is a category within the grammar used to designate all kinds of subject or object.
Also to the noun it is known as the name because that is precisely one of its primary functions, naming different types of beings.
There is a varied universe of nouns which will deal with detail below with their corresponding function.

Classification of nouns

The nouns are those that are used when naming of particular mode to a person or an object. Maria, Europe, Italy are proper nouns. One of the salient features of these is that it must always be written with initial capital letter. Failure to observe this orthographical rule involves RAID in a spelling mistake.
Another class are common nouns, which are those who used to call every person, object or animal in general. Man, dog, home, computer, are some examples of these nouns. Normally we use them to describe all the things, people who are used and are with everyday life. The fact that in the case of common nouns is given because it is people who have characteristics that are shared by others and things, i.e., there is one issue that binds them.
Meanwhile, the main difference that they present with those mentioned above, proper nouns, it is that the latter referred to as something unique and not common. Maria is an own noun because it is unique, while the cat is a common noun that refers to a type of domestic mammal with certain characteristics. Now, if we say the cat Mora we will be talking about a cat in particular and unique.
For his part, abstract nouns are those that respond to ideas or feelings. Our senses may not perceive them, such is the case of joy, passion, hatred, happiness, among others.
As other side are concrete nouns that are perceptible by the senses, such is the case of a table, a Chair, a sheet of paper, among others.
Then substantive accountants and accountants do not appear, the first are those plausible in being listed: three chairs, four tables, six pencils, while a non-accountants can not list them in any way.
The collective and individual nouns are another class that called those concerned called a being in particular and those who appoint people who include others of a same class, respectively. So, dog will be a single noun called a being in particular, and Pack will be a collective noun because it is called all dogs.
And finally we have derived nouns and the primitive, being the first of those derived from another word, seafood restaurant, which comes from seafood; and the primitive does not come from any another word, e.g. classroom.