This is a brief list of some of the more popular sites and applications as well as an overview of the social media topic. ["Social Media." Computer Sciences. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 2nd ed. Vol. 3: Social Applications. Detroit: Macmillan Reference USA, 2013. 216-223. Gale Virtual Reference Library.]
"'Blog' is an abbreviated version of 'weblog,' which is a term used to describe web sites that maintain an ongoing chronicle of information. A blog features diary-type commentary and links to articles on other Web sites, usually presented as a list of entries in reverse chronological order. Blogs range from the personal to the political, and can focus on one narrow subject or a whole range of subjects."
Read more at http://codex.wordpress.org/Introduction_to_Blogging
Wiki has been defined as "the simplest online database that could possibly work" that "allows users to freely create and edit Web page content using any Web browser." (What Is Wiki).
You are probably familiar with Wikipedia, "the free encyclopedia that anyone can edit." There are other related wiki projects.