What about Wikipedia?
Just like the other resources listed on this page, Wikipedia is a great resource for basic information on a subject. However, it is not a scholarly source, and very often you cannot use Wikipedia as a cited source in your assignments. This is because the entries can be written by anyone, not necessarily someone who is an expert.
Best uses of Wikipedia:
a starting point for basic information on a topic
Tips for using Wikipedia:
If you find a fact in Wikipedia that you want to use, verify it in a scholarly source (such as the encyclopedias on this page). Also, make use of the references listed in Wikipedia entries - there might be an article there that is useful for your project.