An article is a word that is often used at the beginning of noun phrases. There are three articles in English: Indefinite articles (a/an), definite articles (the), and the zero article. Articles refer to the shared understanding between speakers as to what they are specifying.

Compare these two sentences:

• Shall we meet at a cafe? (any cafe; a particular cafe has not yet been specified)
• Shall we meet at the cafe? (the listener and speaker have a shared understanding of which cafe)

The indefinite article is used when the listener or reader may not share understanding of what is being referred to, for example, the first time the noun is mentioned:

• I met a group of Italian students in town yesterday. (the listener does not know which students)
• You can catch a bus outside the train station. (one bus of many - but which train station is familiar and understood by both the speaker and the listener).

In contrast, the definite article is used for nouns which are familiar to both the speaker and the listener:

• A man was arrested yesterday for bank fraud at one of Europe's biggest banks. The man will appear in court on Wednesday. Two others were arrested by police last year at the bank. (both nouns here refer to something that is clear to the listener).

The definite article is used with superlative adjective + noun:

• The best in the world.
• One of the most difficult grammar points in the English language.

We use the zero article with plural or uncountable nouns when talking in general:

• Teachers work long hours.
• The post World War II consensus led to the growth in international development.

The zero article is used before institutions (such as school, university, hospital, prison), most countries, place names and dates, times and months:

• The crash victims were taken to hospital in Glasgow.
• Students typicially start university in September in Britain.