Optical disk and Storage device

Optical disk noun - A disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface.

Storage device and optical disk are semantically related. In some cases you can use "Storage device" instead a noun phrase "Optical disk".

Storage device noun - A device that preserves information for retrieval.

Optical disk and storage device are semantically related. Sometimes you can replace phrase "Optical disk" with "Storage device", this phrases are similar.