In "The Tipping Point" Malcolm Gladwell is arguing that the spread of cultural trends can be compared with the spread of disease in an epidemic. In a disease outbreak, there's often a "tipping point" a point at which the virus or bacteria start spreading much more rapidly than before, often with no obvious cause for the change. Malcolm Gladwell argues you can track the spread of many movements in any society in the same way.
As any epidemiologist would look not only for the cause of the disease, Gladwell analyzes how these trends arise and how they become insinuated into the public consciousness. He identifies three groups of people who are essential to the creation and spread of such ideas : Connectors, Mavens, and Salesmen and describes how they can cause ideas to spread.When connectors, mavens, and salesmen are all involved into an idea, it has a much higher chance of spreading. Vice versa, if you have an idea or a product that needs adoption, it might very well be valuable to identify and target these three types of people separately to push for a better adoption of what you are aiming to spread.

http://review-online.blogspot.com/2007/04/tipping-point.html