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 authoring content. 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.

7. Finding information through keyword search.

8. Links

9. Connects information together into a meaningful information ecosystem using the model of the Web, and provides low-barrier social tools.

10. Authoring

11. The ability to create and update content leads to the collaborative work of many rather than just a few web authors. In wikis, users may extend, undo and redo each other's work. In blogs, posts and the comments of individuals build up over time.

13. Categorization of content by users adding "tags" - short, usually one-word descriptions = to facilitate searching, without dependence on pre-made categories. Collections of tags created by many users within a single system may be referred to as "folksonomies"

14. Extensions

15. Software that makes the Web an application platform as well as a document server.

16. Signals

17. The use of syndication technology such as RSS to notify users of content changes.

19. RSS is a family of web feed formats used to publish frequently updated works—such as blog entries, news headlines, audio, and video—in a standardized format.

20. Web feeds benefit publishers by letting them syndicate content automatically. They benefit readers who want to subscribe to timely updates from favored websites or to aggregate feeds from many sites into one place.

22. An Internet forum, or message board, is an online discussion site. It originated as the modern equivalent of a traditional bulletin board, and a technological evolution of the dialup bulletin board system. From a technological standpoint, forums or boards are web applications managing user-generated content

24. A blog is a type of website, usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video.

25. Entries are commonly displayed in reverse-chronological order. "Blog" can also be used as a verb, meaning to maintain or add cont ent to a blog.

27. A social network service focuses on building and reflecting of social networks or social relations among people

28. List of social networks

29. * Facebook * Script

30. * Twitter * Youtube

31. * Flickr * Delicious

32. * My Space * Linked In

34. Facebook is a social utility that connects people with friends and others who work, study and live around th em.

35. Twitter:-

36. Twitter is without a doubt the best way to share and discover what is happening right now.

38. Flickr is almost certainly the best online photo management and sharing application in the world. Show off your favorite photos and videos to the world.

39. Linked in:-

40. LinkedIn (pronounced /ˈlɪŋkt.ˈɪn/) is a business-oriented social networking site. It is mainly used for professional networking.