FAQ General information - What is "disk fragmentation"?
Imagine a book split into several parts, some pages are over here, other pages in another room on another floor altogether. You will have to walk a lot when you need to read the book. It may sound silly, but this is exactly what happens to files on your harddisk. Defragmentation will put all the parts (fragments) back together, making your computer a lot faster.See also:
What is "disk optimization"? Frequently Asked Questions