According to Wikipedia, viral marketing refers to
Marketing techniques that use pre-existing social networks to produce increases in brand awareness or to achieve other marketing objectives (such as product sales) through self-replicating viral processes, analogous to the spread of viruses or computer viruses.
How is viral marketing delivered?
It can be delivered by word of mouth or enhanced by the network effects of the Internet.
What forms can viral marketing take?
Viral marketing may take the form of video clips, interactive Flash games, advergames, ebooks, brandable software, images, or text messages.
What is the goal of viral marketing?
The ultimate goal of marketers interested in creating successful viral marketing programs is to create viral messages that appeal to individuals with high social networking potential (SNP) and that have a high probability of being presented and spread by these individuals and their competitors in their communications with others in a short period of time.