Web 2.0 refers to websites that allow users to interact with each other and change website content, unlike earlier websites that only allowed passive viewing of information. Examples include social media sites, blogs, wikis, video sharing, and applications that combine data from multiple sources. Key features include user-generated content through searching, linking, tagging, and extensions that make the web a platform for applications. Popular social media platforms associated with Web 2.0 include Facebook for connecting with friends, Twitter for sharing what's happening now, Flickr for photo sharing, and LinkedIn for professional networking.