Outside sources that require citations and references include the following:
a. the writer's personal knowledge
b. common knowledge
c. information obtained from the internet
d. all of the above

C. Information obtained from the Internet must be referenced. Common knowledge (info that generally everyone knows) and your own knowledge doesn't have to be cited. I mean, there isn't really anyone to give the credit to anyways, aside from yourself, which would just be given when you put your name as author.