A wiki is software that allows anyone to edit a webpage/article on a website. It is the software that Bloomingpedia uses for its content. The wiki was choosen for Bloomingpedia so that everyone would have a chance to contribute, which leads to its success. Often times, "directory listings" for cities become out of date due to their reliance on a single person to maintain the information. A wiki, on the other hand, can be continuously maintained for as long as visitors to the site care to update it. A community-maintained wiki is a good example of how open source software development works.
Although wiki software was invented in 1995 (WikiBirthday.org), they have become more popular recently for documentation sites and city wikis, like Bloomingpedia.
Its interesting to note here that both the inventor of the wiki, Ward Cunningham and the founder of Wikipedia, Jimmy Wales, both took classes at Indiana University in Bloomington. So its appropriate that Bloomingpedia be a wiki.