article

Grammatical part of speech, used directly before a noun.

There are two articles in English: the definite article the, which is used when a specific thing is being referred to, as in ‘the book that I need’; and the indefinite article a or (before vowels) an, which indicates a single and unidentified noun, as in ‘They gave me a piece of paper and an envelope’.

Some people use the form ‘an’ before the letter h (‘an historic building’); this practice dates from the 17th century, when an initial h was often not pronounced and is nowadays widely considered rather grandiose.