Finding a Wikipedia article on your topic is quite easy and usually involves just typing a search in Google. However, most instructors, and your librarians, don't consider a Wikipedia article to be a credible source.
What is Wikipedia?
Wikipedia is an online encyclopedia based on the premise that anyone can contribute to an article on any topic. Wikimedia, the organization behind Wikipedia, believes that the quality of their articles will improve as more people add or edit content. More eyes translates to better oversight so errors and accuracies will be disappear over time.
So why is Wikipedia not a credible source?
While there is some truth to the notion that given time and multiple contributors the quality of an article should improve it does not always work out this way. Each article won't get the same kind of attention and oversight as ones on more popular topics. Some articles might have few contributors to monitor accuracy of content.
One way to judge the quality of an information source is by the qualifications, experience, and credentials of the author or publisher. Wikipedia contributors are always anonymous so you never know who's contributing to the article.
Articles on controversial topics have been hijacked in the past and the content changed to support specific agendas or viewpoints. Articles subject to vandalization in the past are subject to more control and oversight but this represents just a small fraction of the available articles.
For these reasons we cannot be assured of the credibility of articles from Wikipedia.
You are bound to encounter Wikipedia in your search results anytime you do research on the web. Here are several ways you can make use of it even if you cannot cite it as a source: