A universal media disc, or UMD for short, is a type of small, round disc that is used to store various types of media content, like movies or games. It was primarily used with the Sony PlayStation Portable (PSP) handheld gaming device.
Think of a UMD like a tiny DVD that you can hold in the palm of your hand. Just like a DVD, you put the UMD into a special player, in this case the PSP, to watch a movie or play a game.
What's special about UMDs is that they can hold a lot of data, like a whole movie or a big video game. This is because they use a special kind of technology to compress the data and make it fit on the small disc.
Overall, UMDs were pretty cool and popular back in the day, but they've been mostly replaced by digital media like streaming services and downloadable games.