The Definite Article

The definite article the is used with countable and uncountable nouns.

e.g. the music, the woman, the trees

The is used:

with nouns when we are talking about something specific, that is, when the noun is mentioned for a second time or is already known. In other words, when we can answer the question ‘Who?’ or ‘Which?’ e.g. I received a letter and a postcard on my birthday. The letter was from my parents and the postcard was from my friend.
with nouns which are unique (the Sun, the Moon, the Earth, etc.).
with the names of rivers (the Nile), seas (the Black Sea), oceans (the Indian Ocean), mountain ranges (the Pyrenees), deserts (the Gobi), groups of islands (the Canary Islands) and countries when they include words such as state, kingdom,republic, etc. (the United States).
with the names of musical instruments (the piano, the saxophone) and dances (the tango).
with the names of hotels (the Sheraton Hotel), theatres/cinemas (the Odeon Theatre), ships (theQueen Mary), organizations (the UN), newspapers (The Times) and museums (the Louvre).
with nationality words (the Belgians) and names of families (the Johnsons).
with titles when the name of the person is not mentioned (the Duchess of Kent, the Queen) but: Queen Mary.
with the words morning, afternoon and evening. e.g. He goes home in the evening.

e.g. She went to the station to meet Jim.

with historical periods/events (the Stone Age, the Middle Ages, the First World War) but: World War I.
with the words only, last, first (used as adjectives). e.g. He was the least person to arrive.

e.g. She is the most intelligent woman I’ve ever met. Bob drives the most carefully of all.

The is not used:

with uncountable and plural countable nouns when talking about something in general, that is, when we cannot answer the question ‘Who?’ or ‘Which?’.

e.g. Trees produce oxygen. (Which trees? Trees in general.)

with proper nouns. e.g. This is Tom.
with the names of countries (Egypt), cities (Rome), streets (Oxford Street), parks (Hyde Park), mountains (Mont Blanc), railway stations (Victoria Station), bridges (Tower Bridge), individual islands (Rhodes), lakes (Lake Ontario) and continents (Asia).
with the names of sports, games, activities, days, months, celebrations, colours, drinks, meals and languages (when they are not followed by the word ‘language’). e.g. I speak French. but: The French language is spoken in some parts of Canada.
with the words this/that/these/those (this bag, those cars) NOT: the this bag
with possessive adjectives or the possessive case. E.g. That isn’t my car – it’s Keith’s.
with titles when the person’s name is mentioned (Prince Charles, President Reagan).
with two words names when the first word is the name of a person or place (Luton Airport) but: the White House.

with names of pubs, shops, banks and hotels named after the people who started them and end in –s or –‘s. Harrods, Lloyds Bank, Emma’s pub but: the Black Bull (pub) (because ‘Black’ is not a name of a person or place).

with the words school, church, bed, hospital, college, university, court, prison or home when we refer to the purpose for which they exist. E.g. Jack was in prison. (He was a prisoner.) Jack’s mother went to the prison to see him. (She went to the prison as a visitor.)

with the words home, father/mother when we talk about our own home/parents. e.g. Father is at home.
with means of transport: by bus/car/train/plane, etc. e.g. She travelled by plane.
with the names of illnesses. e.g. He’s got malaria. But: flu/the flu, measles/the measles, mumps/the mumps.