Some extreme compression methods compress the in-game radio or movie cutscenes to lower bitrates, drastically saving space.

: To reach extreme compression, files like cutscenes (FMVs) or high-quality audio are often stripped out.

In the world of ROMs and ISOs, “highly compressed” refers to reducing the file size of a game from its original format (typically 4.7 GB for a DVD) down to a fraction—sometimes just 100 MB to 500 MB.