A plastic container that holds a CD or DVD disc for added protection. The bare disc is placed in the caddy, and the caddy is inserted into the drive. A caddy is not a jewel case. A jewel case protects the disc for transportation. A caddy protects the disc while reading and writing. See HDD cradle
Earlier drives always used a caddy. Today, some drives still require one for added protection.
DVD-RAMs use a Caddy
For writing, DVD-RAM drives require the disk to be placed into a caddy. The drives support both caddy and caddyless media, and for reading, the bare disks can be used. (Image courtesy of Panasonic Industrial Company.)