Answer:
A virtual world is where you make a boy or girl and think of a username and password,you can walk around places and add friends to your friend list and chat to them in public or sometimes private,you can also make your own house and decorate it and buy pets for protend money,(sometimes you have to pay to get money for it) often you can become a member of a virtual world so you get to do more things and buy more different stuff.
Basically a virtual world is like our real world but on a computer/laptop screen where you makke a person and do the same fun things we do right now!
I hope I have helped you,good virtual worlds you could try out is:
Club penguin for 5-12 year olds
Habbo for 13-20 year olds
have fun!