Bibliographic or reference material that documents the SOURCE of a quote or piece of evidence that you have found.
The act of citing is to record the source of a quote or other piece of information. Doing so enables yourself and others to make decisions about the reliability of the information. The more authoritative (or well recognized) the source is, the better. For example, a piece of information that you obtained from Encyclopedia Britannica, might be seen as more reliable than information gathered from someone's personal website.
There are multiple ways to cite a reference, but you can also create your own citation style and use what works for you within your own research. - As long as you are consistent. Consistency is the key! If you wish to formally publish your research, you will most likely need to use a citation style that is accepted by the community that will be reading the material.
The citation tag should be used for questions about formatting citations, inputting citations into software, best practices, etc.