Web 2.0 refers to a number of sites that came to prominence in the mid 2000's that appeared to herald a new era in the functionality and types of interaction available on the web.
Web 2.0 was really a combination of two areas:
2) The birth of the social web. Social sites which allowed sharing of content with large number of users (e.g. flickr, delicious, youtube etc.) came to prominence. Yahoo! Answers can be viewed as a web 2.0 site, as it allowed people to easily create content and interact in a way that didn't exist before.
Whilst web 2.0 fundamentals are still applicable, the internet has really now moved on to a new era where the social web is the centre of most people's experience of the internet. Web 2.0 can be seen as a precursor to this era, which is a more fundamental change that what we saw during the mid 2000s.
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