The Internet is "a vast computer network linking smaller computer networks worldwide. The Internet includes commercial, educational, governmental, and other networks, all of which use the same set of communications protocols." ~ dictionary.com

The World Wide Web is "the complete set of electronic documents stored on computers that are connected over the Internet and are made available by the protocol knows as HTTP. The World Wide Web makes up a large part of the Internet. ~  The American Heritage Science Dictionary

Search engines are "web sites or software that search the internet for documents that contain a keyword, phrase, or subject specified by the user to the search engine. Each engine has it's own method of searching for information. ~ The American Heritage New Dictionary of Cultural Literacy, 3rd ed.

A browser is "a program that accesses and displays files and other data available on the internet and other networks. Entering a website's URL in the address window of a browser will bring up that website in the browser's main window." The American Heritage Science Dictionary

A blog is "an online diary; a personal chronological log of thoughts published on a Web page; also called a weblog; typically updated daily, blogs often reflect the personality of the author." ~ dictionary.com

A wiki is "any collaborative website that users can easily modify via the web, typically without restriction. A wiki allows anyone, using a web browser, to edit, delete or modify content that has been placed on the site, including the work of other authors..."Wiki" means quick in Hawaiian." The Free On-line Dictionary of Computing

Twitter is "a free internet computer service for posting short messages, known as 'tweets', via a single server, which are then sent to all users who have chosen to follow you or a specific user." ~ The Free On-line Dictionary of Computing