You're probably familiar with the very common Spanish words un and una, which are used before nouns and are the equivalent of "a" or "an" in English. These words are known as singular indefinite articles.
In Spanish, these words can also exist in the plural form; unos and unas are known as the plural indefinite articles. Although they don't have an exact English equivalent, they are usually translated as "some" or "a few"; if one is used before a number, it usually means "about" or "approximately." Like adjectives, the article must agree with the noun in number and gender. See examples of the plural indefinite article in these sample sentences:
- Compré unas manzanas. I bought a few apples.
- Unos alumnos salieron. Some students left.
- Tengo unos casetes nuevos. I have some new cassettes.
- La película duró unos noventa minutos. The film lasted about 90 minutes.
- Tomamos unos refrescos. We had some soft drinks.
- Necesité unas horas para leer el libro. I needed a few hours to read the book.
As is the case with singular indefinite articles, the plural article is needed before each of the items in a series: Compré unas manzanas y unas peras. I bought some apples and pears.
If unos or unas is used before an item that exists in the plural to refer to a single object (as "pants" or "glasses" in English), the article can mean "one" or "one pair": Necesito unas gafas de buceo. I need a pair of diving goggles.