Term: volume (disk)

A volume is a logical unit of disk storage, most commonly (in Windows, at least) associated with a single drive letter.

The most important difference between the terms “volume” and “partition” is that volume is a logical construct and does not imply any physical attributes, whereas a partition refers specifically to physical layout. A single volume (perhaps a C: drive) could:

Take up an entire disk.
Take up only a portion of a disk.
Be spread across several disks.

Volumes contain folders, which in turn contain files, which in turn contain data.

While it’s exceptionally common to refer to a volume as a “disk”, (e.g. the “C:” disk), very technically that’s inaccurate, as “disk” more properly refers to the physical media. Since the majority of volumes are contained on a single disk, and most commonly a single disk contains only one volume, the terms are often used synonymously.