To get this game into a "highly compressed" state, the file format is changed from a standard disc image to a compressed one.
In the PSP homebrew community, "highly compressed" typically refers to files. socom fireteam bravo 3 psp highly compressed exclusive
In the context of the PSP, "highly compressed" usually refers to game files converted into formats like CSO (Compressed ISO) to save space on memory sticks. To get this game into a "highly compressed"