The Web 2.0 is a term used to refer to various technologies and social uses of the World Wide Web emerging from 2004 onwards that emphasize online collaboration, sharing, and interactivity between various users and data. Thus rather than the Web being primarily a place where data is accessed, but rather is also a place where people are interacting and sharing directly, as well as where people are uploading content, annotating content, and the like in a constant stream of bidirectional activity that is itself embedded within multiple social relationships being formed and negotiated online. Key terms include social networking, Wikis, folksonomies, social bookmarking, RSS feeds, podcasts, social software, and the like.
THDL fully embraces the fundamental principles of THDL 2.0 technically in its use of such technologies as Ruby on Rails and Ajax, and practically in terms of its efforts to provide online workspaces and tools for generating data, annotating data, self-expression, distributed generation of data, and community formation. Thus THDL aspires to be a Library not just in the sense of a place where people access data, but a Library as a community center where people come together, work together, and dynamically grow together.
See the Wikipedia article on Web 2.0 for a short introduction.