Web 2.0 is just a catch phrase meant to group together design, style and business ideas after the dot-com crash of the early 2000s. By calling it Web 2.0 it sounds like a new idea and it may attract investment capital to companies that say that they are Web 2.0 hip. Sometimes it's used to describe user created content communities which are also called the second wave of the internet. Check Wikipedia for a more detailed explanation: http://en.wikipedia.org/wiki/Web_2.0