before a consonant: [ˈðə], before a vowel: [ˈðiː]

WordReference Collins English Usage © 2019
basic uses
The is called the definite article. You use the at the beginning of a noun phrase to refer to someone or something that has already been mentioned or that is already known to the hearer or reader.
A man and a woman were walking on the beach. The man wore shorts, a T-shirt, and sandals. The woman wore a bright dress.
You can add a prepositional phrase or a relative clause when you need to show which person or thing you are talking about.
I've no idea about the geography of Scotland.
That is a different man to the man that I knew.
You use the with a singular noun to refer to something of which there is only one.
They all sat in the sun.
The sky was a brilliant blue.
types of thing or person
You can use the with the singular form of a countable noun when you want to make a general statement about all things of a particular type.
The computer allows us to deal with a lot of data very quickly.
My father's favourite flower is the rose.
Be careful
You can make a similar statement using a plural form. If you do this, don't use ‘the’.
It is then that computers will have their most important social effects.
Roses need to be watered frequently.
Don't use ‘the’ with an uncountable noun when it is used with a general meaning. For example, if you are talking about pollution in general, you say ‘Pollution is a serious problem’. Don't say ‘The pollution is a serious problem’.
We continue to fight crime.
People are afraid to talk about disease and death.
You can use the with words such as rich, poor, young, old, or unemployed to refer to all people of a particular type.
Only the rich could afford his firm's products.
They were discussing the problem of the unemployed.
Be careful
When you use one of these words like this, don't add ‘-s’ or ‘-es’ to it. Don't say, for example, ‘the problem of the unemployeds’.
You can use the with some nationality adjectives to refer to the people who live in a particular country, or to a group of people who come from that country.
They depend on the support of the French.
Nationality words
systems and services
You use the with a singular countable noun to refer to a system or service.
I don't like using the phone.
How long does it take on the train?
You don't usually use ‘the’ between a preposition and a word like church, college, home, hospital, prison, school, or university.
Will we see you in church tomorrow?
I was at school with her.
➜ See church
➜ See college
➜ See home
➜ See hospital
➜ See prison
You don't usually use ‘the’ in front of the names of meals.
I open the mail immediately after breakfast.
I haven't had dinner yet.
used instead of a possessive
You sometimes use the instead of a possessive determiner, particularly when you are talking about something being done to a part of a person's body.
She touched him on the hand.
He took her by the arm and began pulling her away.
Possessive determiners
used with superlatives and comparatives
You usually use the in front of superlative adjectives.
We saw the smallest church in England.
You don't usually use ‘the’ in front of superlative adverbs.
They use the language they know best.
You don't usually use ‘the’ in front of comparative adjectives or adverbs.
The model will probably be smaller
I wish we could get it done quicker
However, there are a few exceptions to this.
Comparative and superlative adjectives Comparative and superlative adverbs
'the' also found in these entries:

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