Wikipedia
The concept of human knowledge was limited to the combined information that experts in certain fields of study had. Wikipedia, being a global online encyclopedia that can be edited by anyone, has changed this notion. Instead of relying on the intricate knowledge of the few, Wikipedia relies on the general knowledge of the common man. By doing this, Wikipedia is able to be updated constantly, reflecting changes in technology and culture.
What I mean by reflecting changes in culture is Wikipedia updates with new technologies, policies, and terminology. For instance, try looking up the word "cracker" in an encyclopedia. You will probably find a description of a graham cracker or derivative thereof. On Wikipedia, you will find multiple definitions, in particular its use as a racial term. For a technology, try opening a Funk & Wagnall's and looking up Lasik. You won't find it. Wikipedia goes to great lengths to detail the procedure (Lasik is laser eye surgery), as well as provide hyperlinks to related topics, such as eye structure or instruments that are used.
An encyclopedia used to be a collection of knowledge confirmed by experts printed in book form. Most encyclopedias contained general knowledge covering a variety of subjects, from countries to tree types. Subject specific encyclopedias do exist, but they attempt to limit the depth of knowledge so that all aspects of the field are covered. So does Wikipedia undermine or improve this concept? Well, it does both.
It undermines the encyclopedia because the encyclopedia contains information collected and confirmed by experts and accredited scholars. People can read the information and know it's reliable. Another purpose of an encyclopedia is to compress knowledge from many areas into a single book of reasonable size. Wikipedia, while it contains all the information in one source, it is hardly a reasonable size. Also, an encyclopedic book is much more portable than Wikipedia.
Although it undermines an encyclopedia in those two regards, it improves on the encyclopedia in significant ways. First, all information is compiled into one source. It may lack portability, but almost all subjects are covered in here. If they aren't covered to the depths you want, Wikipedia provides links to other sites or articles that contain more information. Second, anyone can contribute to it. Experts may not have the time to add new information as it develops to Wikipedia, so the common person must do it. The only downside to this is that you have to cross reference any information found on Wikipedia with another source to ensure it's valid. Anyone can edit Wikipedia, so there is no guarantee the information is accurate.
Lastly, Wikipedia updates on the fly, and it is online. New information surfaces every day, and older information becomes obsolete. Wikipedia allows old information to be removed and new information to be entered, and when it's submitted the changes are displayed almost immediately. A normal encyclopedia is only printed once every few years (if you're lucky it will be printed annually), and a lot of information changes in that time. The fact that Wikipedia is online, and since internet access is available almost anywhere, makes it easily accessible. As an aside, Wikipedia is offered in multiple languages; most encyclopedias are not.
Wikipedia and other online libraries change the notion of publishing knowledge from an esoteric practice to a public effort. Granted, most people aren't qualified to provide reliable information on any one subject, which reduces the reliability of information. But most people only write about what they know. There are things in the world that only a few people know, and unless online resources like Wikipedia exist no one else would ever know about them.
