The definite article the is the most frequent word in English.
定冠词the是英语中最常用的单词。

We use the definite article in front of a noun when we believe the hearer/reader knows exactly what we are referring to.
当听的人和读者确切知道我们指得是什么时，我们用定冠词the修饰名词。

because there is only one:
因为是唯一的：

The Pope is visiting Russia.

The moon is very bright tonight.

The Shah of Iran was deposed in 1979.

This is why we use the definite article with a superlative adjective:
这就是为什么用定冠词修饰最高级：

He is the tallest boy in the class.

It is the oldest building in the town.

because there is only one in that place or in those surroundings:

because we have already mentioned it:
上文中已提及过：

A woman who fell 10 metres from High Peak was lifted to safety by a helicopter. The woman fell while climbing.一个女人从高峰上向下摔了10米，直升飞机将其救起。这个女人是正在登山的时候掉下来的。

The rescue is the latest in a series of incidents on High Peak. In January last year two men walking on the peak were killed in a fall.这次救援是在高峰上发生的一系列事故中最近的一次。在去年的一月，两个男人在登山时坠落身亡。

We also use the definite article: to say something about all the things referred to by a noun:
定冠词与某一名词连用，代表了一类人或事:

The wolf is not really a dangerous animal (= Wolves are not really dangerous animals)

The kangaroo is found only in Australia (= Kangaroos are found only in Australia)

The heart pumps blood around the body. (= Hearts pump blood around bodies)

We use the definite article in this way to talk about musical instruments:
我们用定冠词修饰乐器：

Joe plays the piano really well.(= George can play any piano)

She is learning the guitar.(= She is learning to play any guitar)

• With adjectives like rich, poor, elderly, unemployed to talk about groups of people:
定冠词与某形容词连用，也可代表一类人：

Life can be very hard for the poor.

I think the rich should pay more taxes.

She works for a group to help the disabled.

The definite article with names:

We do not normally use the definite article with names:
名字前一般不会用定冠词the：

William Shakespeare wrote Hamlet.

Paris is the capital of France.

Iran is in Asia.

But we do use the definite article with:
但是在专有名词前要用定冠词the：

countries whose names include words like kingdom, states or republic:
如国家名中包括王国、合众国或者共和国等

the United Kingdom; the kingdom of Nepal; the United States; the People’s Republic of China.

countries which have plural nouns as their names:
国家名中含有复数名词的：

the Netherlands; the Philippines

geographical features, such as mountain ranges, groups of islands, rivers, seas, oceans and canals:
地貌特征如山系、岛屿、河流、海洋或者运河：

the Himalayas; the Canaries; the Atlantic; the Atlantic Ocean; the Amazon; the Panama Canal.

newspapers:
报纸：

The Times; The Washington Post

well known buildings or works of art:
有名的建筑或者艺术品：

the Empire State Building; the Taj Mahal; the Mona Lisa; the Sunflowers

organisations:
组织结构：

the United Nations; the Seamen’s Union

hotels, pubs and restaurants*:
宾馆、酒吧和饭店：

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.
注意：如果宾馆或者饭店是以其经营者命名的，我们不用定冠词进行修饰。

families:
家族：

the Obamas; the Jacksons