Definition - Nouns are 'names' we use to identify people, things, places, or ideas.
Examples of Spanish nouns are:
             • Carlos [Charles], maleta [suitcase], sobre [envelope], España [Spain], valor [courage], ...

Types - Nouns can be of several different types.

Proper nouns are names of specific people, things, locations, or ideas:
             • Ana [Ann], las Naciones Unidas [the United Nations], Cuba [Cuba], las Cortes [Spanish Parliament], ...

Common nouns are names of general 'categories' of people, objects, places, or concepts:
             • chico [boy], organización [organization], ciudad [town], belleza [beauty], ...

Countable nouns are names of anything that can be counted:
             • una maleta [one suitcase], tres sobres [three envelopes], muchas gracias [many thanks], ...

Uncountable nouns name what cannot be counted:
             • vino [wine], aire [air], agua [water], ...

Note: some nouns can be used as countable or uncountable depending on what we want to say.
Examples of uncountable nouns:
             • La cerveza alemana es buena. [German beer is good.]
             • Esto es café. [This is coffee.]
Examples of uncountable nouns used with a 'countable meaning':
             • Cuatro cervezas cuestan dos euros. [Four beers -- glasses/cans/bottles/... of beer -- cost two Euros.]
             • Bebo un café. [I drink a coffee -- cup of coffee.]

Collective nouns refer to a group made up of more than one person or thing:
             • gente [people], familia [family], fruta [fruit], rebaño [herd], ...

Gender - Some languages divide nouns according to gender. In Spanish there are two genders: masculine and feminine.
This concept is not easy to understand for speakers of languages that do not have genders, especially because the genders of nouns do not follow a clear logic. Some nouns that name masculine people or things are masculine, but others are feminine, and vice versa. Trying to 'reason' about the gender of a noun is not very helpful. The best is to simply learn the gender of the nouns by learning other words that indicate gender, for instance the articles.

Examples of Spanish nouns divided by gender:
             • Masculine - el libro [the book], el idioma [the language], el sobre [the stamp], el país [the country]
             • Feminine - la maleta [the suitcase], la mano [the hand], la calle [the street], la ciudad [the town]

Number - Most nouns have a singular and a plural form. Singular refers to one (only one person, thing, or 'group'), while plural refers to more than one.

Examples of singular and plural form:
             • Singular - una chica [a girl], un euro [one Euro], un país [a country]
             • Plural - dos chicas [two girls], cien euros [hundred Euros], muchos países [many countries]