A noun is a kind of word (see part of speech) that is usually the name of something such as a person, place, thing, animal, or idea. In English, nouns can be singular or plural.

Nouns often need a word called an article or determiner (like the or that). These words usually do not go with other kinds of words like verbs or adverbs. (For example, people do not also describe nouns). In English, there are more nouns than any other kind of word.

Every language in the world has nouns, but they are not always used in the same ways. They also can have different properties in different languages. In some other languages, nouns do not change for singular and plural, and sometimes there is no word for the.

Examples of nouns: time, people, way, year, government, day, world, life, work, part, number, house, system, company, end, party, information.

History 
The word noun comes from the Latin nomen meaning "name." Words like nouns were described in early days by the Sanskrit grammarian Pāṇini and ancient Greeks like Dionysios Thrax.

Uses of nouns 
In English sentences, nouns can be used as a subject, object, or complement. They often come after prepositions, as the 'object of preposition'.

Nouns can sometimes describe other nouns (such as a soccer ball). When they do this, they are called modifiers or adjuncts.

There are also verb forms that can be used in the same way as nouns (such as 'I like running.')  These are called verbals or verbal nouns, and include participles (which can also be adjectives) and infinitives.

Specificness 
Nouns are classified into common and proper. Pronouns have commonly been considered a different part of speech from nouns, but in the past some grammars have included them as nouns as do many modern linguists.

Proper nouns 
Proper nouns (also called proper name) are specific names. Examples of proper nouns are: London, John, God, October, Mozart, Saturday, Coke, Mr. Brown, Atlantic Ocean. Proper nouns are individual things with names, not general nouns.

Proper nouns begin with an upper case (capital) letter in English and many other languages that use the Roman alphabet.  (However, in German, all nouns begin with an upper case letter.) The word "I" is really a pronoun, although it is capitalized in English, like a proper noun.

Some common nouns (see below) can also be used as proper nouns. For example, someone might be named 'Tiger Smith' -- even though he is not a tiger or a smith.

Common nouns 
Common nouns are general names. Sometimes the same word can be either a common noun or a proper noun, depending on how it is used; for example:
 there can be many gods, but there is only one God.
 there can be many internets (two or more networks connected together), but the largest internet in the world is the Internet.

Countability 
In English and many other languages, nouns have 'number'. But some nouns are only singular (such as furniture, physics) and others are only plural (such as clothes, police). Also, some nouns are countable (for example, one piece, two pieces) but others are uncountable (for example, we do not say one furniture, two furnitures).

The plural form of most nouns is created simply by adding the letter(s) -(e)s.

 more than one snake = snakes
 more than one ski = skis
 more than one Barrymore = Barrymores

Despite plural forms being written using the letter(s) -(e)s, the pronunciation of the letter(s) will pronounced as /-s/, /-z/, or /-ız/ depending on which type of phoneme, or unique sound, comes before it. These variations of the plural morpheme are called allomorphs.

Some dictionaries list "busses" as an acceptable plural for "bus". Presumably, this is because the plural "buses" looks like it ought to rhyme with the plural of "fuse," which is "fuses." "Buses" is still listed as the preferable plural form. "Busses" is the plural for "buss," a seldom used word for "kiss."

There are several nouns that have irregular plural forms. Plurals formed in this way are sometimes called mutated (or mutating) plurals.
 more than one child = children
 more than one woman = women
 more than one man = men
 more than one person = people
 more than one goose = geese
 more than one mouse = mice
 more than one deer = deer
more than one ox = oxen
more than one tooth = teeth

Many of the above irregular plural forms stem from Old English, which had more complex rules for making plural forms.

And, finally, there are nouns that maintain their Latin or Greek form in the plural. 
 more than one nucleus = nuclei
 more than one syllabus = syllabi
 more than one focus = foci
 more than one fungus = fungi
 more than one cactus = cacti (cactuses is acceptable)
 more than one thesis = theses
 more than one crisis = crises
 more than one phenomenon = phenomena
 more than one index = indices (indexes is acceptable)
 more than one appendix = appendices (appendixes is acceptable)
 more than one criterion = criteria
 more than one octopus = octopedes is correct (as the word is Greek: ὀκτώποδες). However, octopuses is acceptable, more used and simpler.

Possessives 
Nouns are words for things, and since things can be possessed, nouns can also change to show possession in grammar. In English, we usually add an apostrophe and an s to nouns to make them possessive, or sometimes just an apostrophe when there is already an s at the end, like this:
 This is Sam. This is Sam's cat.
 The woman's hair is long.
 There are three cats. The cat's mother is sleeping.

How adjectives become nouns 

Most adjectives become nouns by adding the suffix -ness. Example: Take the adjective 'natural', add 'ness' to get 'naturalness', a noun. To see a list of 100 adjectives used in Basic English, click here.

Word order in noun phrases 
A noun phrase is a phrase where the head word is a noun. In English, the word order of most noun phrases is that determiners, adjectives, and modifying nouns in respective order must appear before the head word, and relative clauses must appear after the head word.

References 

English grammar by Sachin Jadhavar {ISBN 978-81-949383-2-3}

Other websites
Nouns

Parts of speech