4. because we have already mentioned it:
A woman who fell 10 metres from High Peak was lifted to safety by a helicopter.
The woman fell while climbing
5. to say something about all the things referred to by a noun:
The wolf is not really a dangerous animal (= Wolves are not really dangerous
animals
6. We use the definite article in this way to talk about musical instruments:
Joe plays the piano really well.(= Joe can play any piano)
7. to refer to a system or service:
I heard it on the radio.
8. With adjectives like rich, poor, elderly, unemployed to talk about groups of people:
Life can be very hard for the poor.
9. Countries whose names include words like kingdom, states or republic:
the United Kingdom; the Kingdom of Nepal; the United States; the People’s Republic of China.
10. Countries which have plural nouns as their names:
the Netherlands; the Philippines
11. Geographical features, such as mountain ranges, groups of islands, rivers, seas, oceans and canals:
the Himalayas; the Canaries; the Atlantic; the Atlantic Ocean; the Amazon; the Panama Canal.
12. Newspapers:
The Times; The Washington Post
13. Well known buildings or works of art:
the Empire State Building; the Taj Mahal; the Mona Lisa; the Sunflowers
14. Organisations:
the United Nations; the Seamen’s Union
15. Hotels, pubs and restaurants*:
the Ritz; the Ritz Hotel; the King’s Head; the Déjà Vu
*Note: We do not use the definite article if the name of the hotel or restaurant is the name of the owner, e.g.,Brown’s; Brown’s Hotel; Morel’s; Morel’s Restaurant, etc.
16. Families:
the Obamas; the Jacksons
Zero article
When we talk about things in general we usually use a plural noun or an uncountable noun with no article.
Kangaroos live in Australia.
BUT
We went to the zoo and saw the kangaroos. These are particular kangaroos – not kangaroos in general.