A clever form of marketing in which the user is actually promoting the company that provides a service. Here's an example of how it works: When you send an e-card to someone, he or she has to go to a particular Web site to look at it. This makes you, the e-card sender, a marketer for that company, because you are suggesting that other people should go to this site and use this service. Furthermore, each recipient of an e-card becomes a potential marketer for the company, just as the initial sender is. So, viral marketing is like a virus that spreads. It's a variation on "word of mouth," a coveted form of marketing that can spread at record speed.