Dave Balter, founder of BzzAgent, does a great job in defining the differences in Buzz, Viral and Word of Mouth Marketing in this edition of ChangeThis. Here are excerpts with Dave's great definitions:
What is Word of Mouth Marketing?
Word of Mouth Marketing (WOMM) is the most powerful medium on the planet. It's the actual sharing of an opinion about a product or service between two or more consumers. It's what happens when people become natural brand advocates. It's the holy grail of marketers, CEOs and entrepreneurs, as it can make or break a product. The key to its success: it's honest and natural.
What is Viral Marketing?
Viral Marketing is an attempt to deliver a marketing message that spreads quickly and exponentially among consumers. Today, this often comes in the form of an email message or video. Contrary to alarmists' fear, viral isn't evil. It isn't dishonest or unnatural. At its best, it is word of mouth enabled, and at its worst, it's just another interruptive marketing message.
What is Buzz Marketing?
Buzz Marketing is an event or activity that generates publicity, excitement, and information to the consumer. It's usually something that combines a wacky, jaw-dropping event or experience with pure branding, like tattooing your forehead (or your ass, as a NYC health club recently did). If buzz is done right, people will write about it, so it essentially becomes a great PR vehicle.
Here's an exceptional infographic on Word of Mouth Marketing (WOMM) from Lithium: