Spindle
1. A post that holds a reel of magnetic tape or CDs.
In the picture to the right, is an example of a blank CD spindle. When
purchasing blank discs they'll often be sold in a spindle like the one shown
here.
2. In the case of a hard disk drive, as seen in the below picture, the spindle is what holds a hard disk drives platters in place. With a traditional hard disk drive there is the need to have multiple platters. The spindle holds these platters in a fixed position with enough space for the read/write arms to get to the data on the disks.
Also see: CD definitions, Hard disk drive definitions, Tape definitions