spindle
A spindle is a shaft that holds rotating hard disk drive (HDD) platters in place. The term is also often used to refer to a single HDD.
Spindle speed, measured in rotations per minute (RPM), is one metric used to gauge disk drive performance. Spindle speed can affect seek time, which is the speed at which a drive can locate a single bit of information, as well as the sustained rate at which data can be read from, or written to, a disk.