: As mentioned, this file extension is associated with CHD (Compressed Hard Disk) files, which are used to store hard disk images. In the context of MAME and similar emulators, CHD files can contain data necessary for emulating arcade games, such as ROMs (read-only memory) and disk images.
This denotes the .
: This suggests that the version of the game or its data is from the United States, possibly indicating a region-specific version or release. Looney Tunes - Sheep Raider -USA- -EnFrEsPt-.chd