Fragmentation occurs when a piece of data is broken up into many pieces that are not stored close together. This can happen when files are saved or deleted on a computer's hard drive. As files are created, modified, and deleted, the space they occupy on the hard drive becomes fragmented, meaning that parts of the file are scattered in different locations. This can lead to slower access times for the data, as the computer has to search for and retrieve the different fragments. Defragmentation is the process of rearranging the fragments of data on a hard drive to optimize performance.