Virtual worlds are three dimensional environments in which you can interact with others and create objects as part of that interaction. How do you do that? You appear as an avatar in the virtual world: an avatar is a virtual representation of you (a 'virtual ego') which can take on any shape or form as you so wish.
There are a range of virtual worlds to choose from which include fantasy, sport, historical and science fiction. Some are loosely based upon the real world but others such as fantasy worlds are as the name says: they are completely disconnected from the real world which is also part of their attraction.
With virtual worlds, men appear as women and vice versa. Some people choose an animal as their alter ego. Whatever you choose the aim is to socially interact with other people in new and exciting ways. This all adds to the experience.
You can communicate with another person using text, sound, graphical images and gesture. Some of the more advanced worlds allow you to use voice or touch.