used to identify a specific person or thing observed or heard by the speaker

that's his wife over there

hello, is that Ben?

referring to a specific thing previously mentioned, known, or understood

that's a good idea

what are we going to do about that?

used in singling out someone or something and ascribing a distinctive feature to them

it is part of human nature to be attracted to that which is aesthetically pleasing

his appearance was that of someone used to sleeping on the streets

expressing strong agreement with a description just given

‘He's a fussy man.’ ‘He is that.’

used instead of ‘which’, ‘who’, ‘whom’, or ‘when’ to introduce a defining clause, especially one essential to identification

the woman that owns the place

the book that I've just written

the year that Anna was born

used to identify a specific person or thing observed or heard by the speaker

look at that chap there

how much are those brushes?

referring to a specific thing previously mentioned, known, or understood

he lived in Mysore at that time

seven people died in that incident

used in singling out someone or something and ascribing a distinctive feature to them

I have always envied those people who make their own bread

referring to a specific person or thing assumed as understood or familiar to the person being addressed

where is that son of yours?

I let him spend all that money on me

Dad got that hunted look

to such a degree; so

I wouldn't go that far

introducing a subordinate clause expressing a statement or hypothesis

she said that she was satisfied

it is possible that we have misunderstood

expressing a wish or regret

oh that he could be restored to health