An indefinite noun is a type of noun that is not specific in its reference. In general, indefinite parts of speech are words that don’t reference a given instance, but to a generic or open instance of a word. Observing the difference between definite and indefinite nouns can help language beginners understand more about a language.
Experts describe an indefinite noun as a noun that doesn’t refer to something that is known or familiar, but to something that is theoretical or random. For instance, an English speaker who refers to "a dog" or "a cat" is using indefinite nouns to refer to any dog or cat. The same speaker referring to “the dog,” or saying a particular dog’s name, is talking about a definite dog. Likewise, talking about “the cat,” or referring to the cat by name replaces an indefinite noun with a definite one.
One of the prime ways to designate indefinite nouns in English is that, rather than using a name or the definitive article the before the noun, the indefinite noun uses the indefinite article, “a” or “an.” These articles usually help listeners or readers determine whether a noun is definite or indefinite. These articles often provide a helpful road map to how to use nouns in context. In English and other languages, thinking about definite and indefinite verbs can also help language learners to figure out more about how native speakers use a particular set of articles. Since articles in some languages are gendered or otherwise complex, separating definite and indefinite nouns and the articles that go with them can be critically important to a language learner; likewise, some languages do no employ articles at all, meaning that other context clues must be used to determine the intended meaning.
Knowing the difference between definite and indefinite nouns is important for those who want to be able to contextualize nouns properly. Some linguists study the acquisition of these noun types in children as a measurement of how easy or difficult it may be too deal with these two different noun categories. Those who are learning a language need to be aware of how definite and indefinite nouns change the meaning of a sentence in order to use them correctly. This can be done with practice. Using resources like textbooks or phrase lists to model correct usage of the various nouns and articles that are common in a language, to refer to both definite and indefinite subjects and objects, is especially helpful.