Special pieces of software can be used to make a PS2 multi-regional or region free. They come in the form of disks which can be loaded into the PS2. When run, they install a codec on the PS2 that allows DVDs from all regions to be played on the machine.
Usually, PS2s are coded to the same region in which they are intended to be sold, so an American PS2 plays only Region 1 DVDs, while a European PS2 plays Region 2 discs. However, when a PS2 is made multi-regional, it is able to play DVD releases from all over the world.