A noun is a part of speech which names an object.
Nouns can be divided in:
common: they describe objects or ideas in general Examples: a man, an hour, love, a car etc.
proper: they describe specified objects. Examples: England, John, Jupiter etc.
Other division can be into:
abstract nouns: words naming feelings or ideas: God, love, trust
concrete nouns: words naming a visible object: a man, a car, a tree