Students in Australia can email fellow students in Canada to compare notes on a shared research project about Blue Whales. A model train fanatic in Zimbabwe can join a discussion with like-minded folks anywhere else in the world.
Virtual communities take many shapes, but they all share a number of characteristics.
They allow people with common interests to meet each other, to communicate, and to stay in touch if so desired. You can consider each one of the thousands of Usenet newsgroups as a virtual community of sorts. Most often, each newsgroup has a bunch of regulars who know one other, and who are in the middle of calm conversations or raging debates with friends they've made online. Discovering the existence and depth of this worldwide subculture is a little like discovering a previously unknown continent, teeming with unfamiliar forms of life.