/ ðeɪ; NAmE / pronoun (used as the subject of a verb)
1.
people, animals or things that have already been mentioned or are easily identified :
'Where are John and Liz?' 'They went for a walk.'
They (= the things you are carrying) go on the bottom shelf.
2.
used instead of he or she to refer to a person whose sex is not mentioned or not known :
If anyone arrives late they'll have to wait outside.
3.
people in general :
The rest, as they say, is history.
4.
people in authority or experts :
They cut my water off.
They now say that red wine is good for you.
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WORD ORIGIN
Middle English : from Old Norse their , nominative plural masculine of sá ; related to them and their , also to that and the .