An indefinite pronoun does not refer to any particular person or thing. It is used to talk about people or things in a general way.
Examples are: anybody, one, all, both, some, any, none, everybody, nobody, anyone etc.
Do you know anybody here?
One must do one’s duty.
Nobody knows where he lives.
Somebody will have to take the lead.
Everyone praised him for his good deed.
When an indefinite pronoun is followed by a noun, it becomes an indefinite adjective.
We must die one day.
All men are mortal.
Few people know his whereabouts.
Any child can solve this problem.
To refer back to an indefinite pronoun, we use he or she.
Each one of the boys occupied his seat.
Each one of the girls raised her hand.
When the sex of the person is not clear, we use they to refer back to an indefinite pronoun. In a more formal style, we use the expression he or she.
Nobody likes to lose his or her credit. (Formal)
Nobody likes to lose their credit. (Informal)
Anybody who tries his or her best can do this. (Formal)
Anybody who tries their best can do this. (Informal)
Everybody is unhappy with his or her lot. (Formal)
Everybody is unhappy with their lost. (Informal)
The indefinite pronouns anybody, anyone, each, every and none are singular and should be followed by singular verbs.
Nobody was impressed with his performance. (NOT Nobody were impressed with his performance.)
The indefinite pronouns all, some and few are plural and should be followed by plural verbs.
Some are born great; some achieve greatness; some have greatness thrust upon them.