DVD unlock codes are codes a DVD owner can input using the remote control for the device to remove its regional lock code. The regional lock code prevents a player sold in one region from playing discs manufactured in another region.
Movies on DVD may have different release dates or distribution rights of companies and studios that vary by country. The DVD standard calls for regional locks to prevent players sold in one region from playing discs manufactured in other regions in order to protect these rights. The standard calls for manufacturers to install lock codes in DVD players and discs.
DVD unlock codes remove these locks so that a player made in China, for example, can play a disc made anywhere. However, most manufacturers have abandoned installing locks due to the number of workarounds and their widespread publication, so most DVD players no longer have them.