Web 2.0 refers to the participatory web where users can interact and collaborate to share content online. It includes social networking sites, user-generated content, and websites that emphasize user feedback and involvement. The document discusses how Web 2.0 allows for value creation, patron interaction, participation in online communities, and collaboration. It provides examples of Web 2.0 tools librarians can use, such as blogs, wikis, social bookmarking, photo sharing, video sharing, and online messaging. These tools help librarians communicate and engage with patrons in new ways.