Disk usage may refer to any of the following:
1. Disk usage or used space is a term used to describe the percentage or overall used space of a disk or drive. As more information is saved to the disk or drive, the total disk usage is increased. For example, in the picture below, Windows showing the total Used space and Free space of the drive with the pie chart illustrating that almost half of the drive is used.
A disk's usage should not be confused with the disk capacity.
2. DU or Disk Usage is a Windows Sysinternals command to view disk usage by directory.