UK:*UK and possibly other pronunciationsUK and possibly other pronunciations strong: /ˈðæt/, weak: /ðət/

US:USA pronuncation: IPAUSA pronuncation: IPA/ðæt; unstressed ðət/

US:USA pronunciation: respellingUSA pronunciation: respelling(ᵺat; unstressed ᵺət)

WordReference Collins English Usage © 2020
That has three main uses:
used for referring back
You use it in various ways to refer to something that has already been mentioned or that is already known. When that is used like this, it is always pronounced /ðæt/.
I was so proud of that car!
How about natural gas? Is that an alternative?
used in that-clauses
That is used at the beginning of a special type of clause called a that-clause. In that-clauses, that is usually pronounced /ðət/.
He said that he was sorry.
Mrs Kaul announced that the lecture would now begin.
That-clauses Reporting
used in relative clauses
That is also used at the beginning of another type of clause called a defining relative clause. In defining relative clauses, that is usually pronounced /ðət/.
I reached the gate that opened onto the lake.
Relative clauses
that - those
That and those are used in different ways when you are referring to people, things, events, or periods of time. They can both be determiners or pronouns. In this use, that is pronounced /ðæt/. Those is the plural form of that.
referring back
You can use that or those to refer to people, things, or events that have already been mentioned or that are already known about.
I knew that meeting would be difficult.
‘Did you see him?’ – ‘No.’ – ‘That’s a pity.'
Not all crimes are committed for those reasons.
There are still a few problems with the software, but we're working hard to remove those.
things you can see
You can also use that or those to refer to people or things that you can see but that are not close to you.
Look at that bird!
Don't be afraid of those people.
‘that’, referring to a person
However, you don't usually use that as a pronoun to refer to a person. You only use it when you are identifying someone or asking about their identity.
‘Who’s the woman in the red dress?' – ‘That’s my wife.'
Who's that?
saying when something happened
When you have been describing an event, you can use that with a word like day, morning, or afternoon to say that something else happened during the same day.
There were no classes that day.
Paula had been shopping that morning.
You can also use that with week, month, or year to show that something happened during the same week, month, or year.
There was a lot of extra work to do that week.
Later that month they attended another party at Maidenhead.
‘this’ and ‘these’
This and these are used in some similar ways to that and those.
'that' also found in these entries:

Report an inappropriate ad.