Defrag is short for defragment. Basically, the defragment process takes files that are split into various fragments on a variety of locations (sectors) on your hard drive and rejoins them in one contiguous path. The theory was that if the read/write head that is retrieving the information you requested doesn’t have to skip to another part of the hard drive to complete the. In the olden days (before the year 2000) when hard drives spun at a slower rate, were smaller in size (we kept running out of storage space for our files), had less read/write heads and the computer operating system could only address so many files, defragmenting the hard drive was a regularly recommended maintenance item to allow us to store more information and retrieve it faster. In 2011, not so much. The drives are faster, bigger, have more read/write heads and the operating system is more savvy about finding files. Many technicians (including myself) feel that there is little or no value to defragmenting your hard drive today. You probably would not be hurting the computer, but you would likely see very little improvement in the computer’s function. So save yourself time and effort by not defragmenting your computer.