A reference is something you can refer to, or something you can use to check things. An encyclopedia like this wikipedia is a fine example of something you could use as a reference. A software manual or the instruction book for a car are other examples of references.

Sometimes the word reference is used to mean "I looked this up, here:" followed by the book and page number or the web page where the information was found.

Reference | Referencia | Refero | Referentia | רפרנט | Ссылка