"Defrag" is a shortened form of the word "defragment," a process of sequencing fragmented data on a hard drive or storage device. Defragmentation allows computers and other electronic storage devices to work more efficiently in general performance, as well as in the retrieving of requested files and sites.
Files become fragmented as they are saved, changed or deleted. Changes to files are occasionally stored in a different area from the original file, resulting in the file and change being fragmented, or kept apart in pieces. As fragmented files become more numerous, they begin to slow the computer's performance, because the file retrievals have to come from several different places.
Computers and devices such as iPads have disk defragmenting tools that, when run, collect and group the fragmented data. In operating systems such as Windows, the disk defragmenting tool offers the option to be either manually run or programmed to automatically run on a schedule.
A different type of computer drive known as a solid-state drive, or SSD, does not need to be defragmented. Solid-state drives perform their own sequencing, and although certain types of data are stored in fragments, they do not take extra time to retrieve files. Solid-state drives do, however, require all other types of basic computer maintenance.