Answer Description

CDfs is the file system used to access the data on Compact Discs (CD). Typically the data are audio tracks.

Wikipedia

CDfs is a virtual file system for Unix-like operating systems; it provides access to data and audio tracks on Compact Discs. When the CDfs driver mounts a Compact Disc, it represents each track as a file. This is consistent with the Unix convention "everything is a file". CDfs supports the following track types: Red Book Compact Disc Digital Audio (CD-DA): Appears as a WAV file; reading from it initiates DAE ripping. White Book Video CD or Super Video CD video: Appears as a playable MPEG-1 file containing audio and video streams. Yellow Book CD-ROM data: Hierarchical File System: Appears as a mountable HFS file system disk image (sans partition table). ISO 9660: Each session appears as a mountable ISO image file. El Torito boot file: Appears as a single bootable disk image file.