A citation style is a strict method of ordering, formatting, and punctuating citation information. Generally, specific citation styles are selected and based on the different information needs of a particular discipline and the different resources that discipline typically uses. In some cases, tradition and longevity of style use can also play a factor in the citation style preference of a discipline.
To assist with with citation styles and their strict requirements for accuracy, citation style guides are an excellent resource for general instructions and examples.