A golden master, or GM, is the final version of a software program that is sent to manufacturing and is used to make retail copies of the software. The golden master follows several other stages in the software development process including the alpha, beta, and release candidate stages. The final release candidate (RC) becomes the "release to manufacturing" (RTM) version, which is also called the golden master.
The term "golden master" has been used by Apple for many years, and is now used by many other software companies as well. It is also used in the video game industry to refer to the final version of games that are sent to replication facilities. When a program reaches the golden master stage, it is often said to have "gone gold." This means it won't be long before the product is available to consumers for retail purchase.
NOTE: Golden master should not be confused with a "gold record," which refers to a music album that has sold 500,000 copies.