"Web
conferencing is used to conduct live meetings or presentations over
the Internet. In a web conference, each participant sits at his or
her own computer and is connected to other participants via the
internet. This can be either a downloaded application on each of the
attendees computers or a web-based application where the attendees
will simply enter a URL (website address) to enter the conference."
-- wikipedia.com
Here's
a list with more information about conferencing tools online. Check it out.