The Wiki site describes Wiki as follows, "A wiki is a database of pages which visitors can edit live." While many people associate Wiki with Wikipedia, there is more to the Wiki family. To name a few, there are Wikianswers (post a question you would like answered), Wikitravel (a travel guide), Wikihow (a how to site), and Wikibooks (textbooks).
Wiki is open editing which means anyone can add and edit information freely. There is a staff that checks these for accuracy. Where there is no support for an entry it is noted. Nonetheless the Wiki sites are a good source of free information from the trivial to the important. For those who remember the "Dallas" television series of the 80s did you know that Patrick Duffy's nephew is former Cy Young award winner Barry Zito of the San Francisco Giants? It's out there on Wikipedia along with other trivial facts.
Wikipedia also was likely the final nail in the coffin for all those encyclopedias that took up much bookcase space. Yes they still sell those encyclopedias just like they still sell vinyl records,cameras that use film and accounting ledger paper but they have been replaced for the most part by improvements in technology.
In closing, a lot of good and useful information can be accessed by going to the Wiki sites. From learning how to fit in while in London to planning your London visit a lot of good information is available just by logging in.