Types of plagiarism
Mixing words or ideas from an unacknowledged source in with your own words or ideas.
Anything you state as a fact must be supported by literature or other forms of statistical data. However, there are certain facts that are so well known, there is no place to cite them. Be careful with common knowledge, however. As the APA blog demonstrates, even the most obvious fact may not be accurate.
Rule of thumb: if you can find the fact without citation in at least five reputable sources, it is probably common knowledge.
Not common knowledge:
When in doubt, cite it!
Courtesy Colorado Technical University.