We should probably look to Wikipedia for a definition of Web 2.0. According to Tim O’Reilly, the guy who termed the phrase, Web 2 is the second generation of web services. It includes a new approach to generating and distributing Web content – which harnesses the power of ‘human connections’. It is characterised by open communication, decentralisation of authority and freedom to share.
Examples of ‘Web 2.0’ include: Wikis (such as Wikipedia – the encyclopedia project where anyone can contribute and edit material, del.icio.us (a social bookmarking site), some blogs and YouTube (the vid sharing site recently bought by Google). Key to all these sites is a ‘decentralisation of authority’ and a ‘sharing’ nature.
Site which don’t take user contributions or allow sharing are stuck in Web 1, and you really don’t want to be seen there!
But Web 2 is getting on a bit now. We have to look forward to the sequel (inspiringly titled – wait for it… Web 3.0), where we will supposedly shop and inhabit ‘virtual worlds’. This diagram from Gary Hayes explains the past and future well. He has much more on his site.