Wikipedia is an enormous encyclopedia that can freely be view and edited by its users. It is constantly being improved and is growing rapidly.
Since Encyclopedia Britannica stopped showing their work gratis online, Wikipedia is now one of the few good alternatives to Google when you need precise unbiased articles as opposed to the unpredictableness of most personal websites or commercial sites listed on Google that provide no useful information.
Go ahead and browse the surprisingly comprehensive reference, and don't be afraid to add your own knowledge.