Disk Defrag (Disk Defragmentation) is the process of uniting and arranging various files on the hard disk of a computer. The hard disk of the computer is like a library. It contains various sections with racks and shelves which contain your important data. When you open any program or access any file on your system, you system will act like the Library assistant. It will search for the file in the millions of racks and shelves and bring it to you or to the program that requested for it.
Imagine a Library where books and papers are spread all over. You will have to look for parts of research in the entire library. It might be ages before you can borrow a single book from such a place. You will have to arrange everything in the Library before you borrow anything from there. Disk Defrag is the same process for a computer. Due to routine computer usage, the data on the disk gets scattered and it is important that this data be arranged once again to make the disk perform better. This process is known as Disk Defrag or Disk Defragmentation because it reduces the fragments from the disk on the computer.
It is recommended that the Disk Defrag should be done at least once a month. A Disk Defrag tool is available with Microsoft Windows, which can be accessed via the properties pane of a Hard Disk, under the Tools tab.