Any reference to any primary law source - case or statute - has a citation. The basic format of a citation is standardized, and generally includes a volume number, an abbreviation of the title of the publication in which the law appears, a page or section number, and a date.
CASES
Court cases are often published by more than one publisher, so there can be more than one citation appearing after the name of the case. Usually the first citation given is to the official reports for a particular court, and is called the "official citation." The official reports are printed by the publisher with which that court has contracted to distribute its cases.
In California the official reports of California Supreme Court cases are published in the California Reports (1st - 4th series) and the official reports of Courts of Appeal cases are published in the California Appellate Reports (1st - 4th series).
The other citations given in a string are known as "unofficial" or "parallel" citations. The text of the opinion is the same in all sources, whether they are "official" or "unofficial."
SUPREME COURT

Court of Appeals

California Supreme Court cases have two parallel citations. The first is to the Pacific Reporter, and the second is to the California Reporter, which started in 1959. Court of Appeals cases have only one parallel citation, to the California Reporter.
STATUTES OR CODES
The terms "statute" and "code" are often used interchangeably. There are two publishers of the California Codes: West and Deering's. The wording of the Codes is identical in either publication; the only difference is in the annotations that follow each section.
The following are examples of citations for California and United States Codes:

List of California Statutory Abbreviations
updated 04/12 kb