The article the is a determiner in a sentence when placed before a noun or a noun phrase. It is called a definite article as it points to a particular person or thing being mentioned in the sentence. It can be used before a singular or a plural noun, and before a countable and an uncountable noun.
We use the determiner the:
to refer to people or things which we know because they have already been mentioned.
- I recognize that man. He's the one who is doing great magic at the marketplace.
- Over there is a cave. There are countless bats roosting in the cave.
to refer to a person or thing when there is only one.
- He is the boss of the company producing pencils.
- The flood occurred only in the east coast of the country.
before superlatives, words such as first, only, etc.
- Peacocks have the most beautiful feathers.
- The first runner to cross the finishing line was a skinny man.
- This duckling is the only pet I have.
before adjectives that act as nouns.
- Sometimes I hate myself for dreaming the impossible.
- They buried the dead wherever they found them.
before a singular noun that is representative of a group of similar people or things.
- A large and flightless bird, the dodo is now extinct.
- The satellite has many uses, the most important of which I think is the transmission of information.
before proper nouns.
- The Robinsons are the latest members of the ghost-hunting club.
- The Niagara Falls is the largest waterfall in the world.