A noun is one of the major Parts of Speech. A good, general, definition of a noun is that it is something which is used to name an object or thing.
car, door, elephant...
There are literally thousands upon thousands of nouns in English and we regularly add new nouns to the list. In the past few years these new nouns have come into English:
internet, social networking, muggle, gaydar...
In English nouns are fairly straightforward and usually have just two forms: singular (i.e. one) and plural (i.e. more than one). In the majority of cases you just add -s to the singular to make it plural:
Look at that beautiful dog!
Look at those beautiful dogs!
For more on this see Singular and Plural Nouns.
The man ate the cake.
The big man ate the cake.
The very big man ate the cake.
The very big Australian man ate the cake.
We have taken a simple noun, man, and added other words to it to make a noun phrase which works (grammatically) in the same way as a single noun.
For more on this see Noun Phrases.
Nouns can be divided into major groups within the category. These come from either how the nouns in the group can be used grammatically or the kind of objects they define.
Some nouns can be counted; you can count the number of books in the room and the number of words on a page, etc. These are countable nouns:
There are fifteen books in the room.
There are over six hundred words on this page.
However, some nouns cannot be counted. You cannot, for example, count water:
* There is one water in the sea.
* There are two waters in the sea.
* We put an asterisk before a sentence to show that it is ungrammatical.
This is because water is a non-countable noun; we cannot put a number in front of it. Non-countable nouns are sometimes known as uncountable nouns or mass nouns.
For more on this, see Countable and Non-Countable Nouns.
Sometimes we use a pronoun to replace a noun in a sentence. We do this so we do not have to repeat the same words again and again. For example instead of saying:
Brian opened the door, Brian paused by the door, and then Brian closed the door quietly.
We can instead say:
Brian opened the door, he paused by it, and then he closed it quietly.
In this case, he is a pronoun which stands for Brian.
For more on this, see Pronouns.
It is easy to see and touch a book and because we can see it and touch it we call it a concrete noun. Sometimes, however, it is impossible to see or touch a noun. For example, these are also nouns but you cannot see or touch them:
love, happiness, life
We call these abstract nouns and they refer to concepts rather than objects.
For more on this, see Concrete/Abstract Nouns.
We also talk about proper nouns which are the names of people or places:
Peter, Buddha, Rome, Mars
In English proper nouns are capitalized.
For more on this, see Proper Nouns.
Sometimes we want to use a verb as a noun. For example, in the following example ski is a verb:
I like to ski.
Skiing is my favorite sport.
When we use a verb as a noun we call it a gerund (or sometimes a verbal-noun).