Viral marketing describes any strategy that encourages individuals to pass on a marketing message to others, creating the potential for exponential growth in the message's exposure and influence. Like viruses, such strategies take advantage of rapid multiplication to explode the message to thousands, to millions.

It doesn't have to be complicated. You've undoubtedly seen those buttons on web sites that say "click here to send this page to a friend." With this simple tactic, your site visitors are able to provide you with "word-of-mouth" advertising for your web site, and each successive visitor can do the same. Word-of-mouth advertising has traditionally been one of the most effective advertising strategies available. The internet does not change that principle, but makes it easier.