The Photon Debugger is a Keyblade acquired after Sora's first trip to Space Paranoids in Kingdom Hearts II. It is given to Sora by Tron after the two of them defeat the Hostile Program before it can destroy Space Paranoids. The Photon Debugger looks similar to the outfits Sora and co. wear while in Space Paranoids. The key chain symbol is a blue disk like the ones Tron uses.
It's name comes from two words, debugging is a way to get rid of virus, and since it is a keyblade, it is meant as a heartless to be a type of virus. Photons are a form of light, and Sora is the wielder of the Keyblade of light.