Web 2.0 refers to second-generation web services that emphasize online collaboration and sharing among users, such as social networking sites, wikis, communication tools, and folksonomies. It is characterized by enabling users to interact and collaborate with each other in a social media dialogue as creators of user-generated content in a virtual community, in contrast to websites where users are limited to the passive viewing of content. Tim O'Reilly is considered a key early proponent of the term and concept of Web 2.0.