An article in grammar is a morpheme, such as an affix, which determines the scope of the described noun. Use of a definite or indefinite article indicates that the noun to which the article refers identifies a specific, already explicitly or inherently identified, referent (in which case the article is a definite article) or that it does not (an indefinite article). Some languages, such as Russian, lack articles.
The English definite article is "the", and the two indefinite articles are "a" and "an". "A" is used before words beginning with a consonant, "an" before words beginning with a vowel. This distinction is phonological — based on the following word as pronounced, not as written; compare, e.g., "an honor" with "a union".
Also considered articles are English words like 'some' (a partitive article) or 'no' (a negative article), although this usage is less common in everyday language, where 'article' usually means a definite or indefinite article.