0 used especially in questions as the subject or object of a verb, when asking which person or people, or when asking what someone's name is: --
1 used as the subject or object of a verb to show which person you are referring to, or to add information about a person just mentioned. It is used for people, not things: --
2 abbreviation for the World Health Organization --
3 used esp. in questions to ask which person or people, or to ask someone’s name: --
Who’s she?
Who did this?
4 used as the subject or object of a verb when referring to a particular person or when adding information about a person just mentioned: --
People who work in the trade can buy their books at a discount.
She's part of a team of scientists who are engaged on/upon cancer research.
There seems to be some confusion over who is actually giving the talk.
Who is the president of France?