Learner's definition of THEY
those people, animals, or things
— used to refer to people in a general way or to a group of people who are not specified
You know what they say: you only live once.
They say it will be a mild winter. [=people who predict the weather say that it will be a mild winter]
She's as hardworking as they come. [=she's extremely hardworking]
They will be holding the graduation outdoors if the weather permits.
They took away his license.
he or she
— used to refer to a single person whose sex is not known or specified