Definition - What does Spinning Disk mean?
A spinning disk is the mechanism within a hard disk drive to which memory is written. With rotating plates attached to an arm that writes the data, the spinning disk mechanism physically resembles a record player (although it is sealed within an enclosure). The plates are magnetized (similarly to cassette tapes) in order to store data that is written using copper heads.
Techopedia explains Spinning Disk
Spinning disk technology has been arguably the most popular form of computer storage for decades, but has been increasingly superseded by solid state drives (which are particularly common in newer notebooks and laptops) in recent years. Nevertheless, the older hard disk technology has dramatically increased its storage throughout the years. In spite of its constant physical size and uniform form factor, higher precision and sophisticated design has allowed the spinning disk hard drive to increase its capacity into the terabyte range.