What was the original PlayStation Portable’s physical game format called?

The original PlayStation Portable used a physical game format called Universal Media Disc.

Universal Media Disc, usually abbreviated UMD, was a small optical disc created for Sony’s portable system. UMDs could hold games and other media, including films and music, and were enclosed in a protective plastic cartridge-like shell.

Sony released the PSP in Japan on December 12, 2004, followed by North America in March 2005 and Europe in September 2005. The system also supported digital downloads stored on Memory Stick media, so not every PSP game was distributed physically on UMD.

UMD is sometimes mistaken for MiniDisc because both were compact Sony optical formats. They were different technologies with different purposes: MiniDisc was primarily associated with recorded audio, while UMD was designed for PSP software and entertainment media.