The Collaborative International Dictionary of English v.0.48:

fragmentation \fragmentation\ n.
   the act or process of separating something into small pieces
   or fine particles.

   Syn: atomization, atomisation.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

fragmentation
    n 1: separating something into fine particles [syn:
         atomization, atomisation, fragmentation]
    2: the disintegration of social norms governing behavior and
       thought and social relationships
    3: (computer science) the condition of a file that is broken up
       and stored in many different locations on a magnetic disk;
       "fragmentation slows system performance because it takes
       extra time to locate and assemble the parts of the fragmented
       file"
    4: the scattering of bomb fragments after the bomb explodes

The Free On-line Dictionary of Computing (30 December 2018):

fragmentation
fragment

   1.  segmentation.

   2. The process, or result, of splitting a large area of free
   memory (on disk or in main memory) into smaller non-contiguous
   blocks.  This happens after many blocks have been allocated
   and freed.  For example, if there is 3 kilobytes of free space
   and two 1k blocks are allocated and then the first one (at the
   lowest address) is freed, then there will be 2k of free space
   split between the two 1k blocks.  The maximum size block that
   could then be allocated would be 1k, even though there was 2k
   free.  The solution is to "compact" the free space by moving
   the allocated blocks to one end (and thus the free space to
   the other).

   As modern file systems are used and files are deleted and
   created, the total free space becomes split into smaller
   non-contiguous blocks (composed of "clusters" or "sectors"
   or some other unit of allocation).  Eventually new files being
   created, and old files being extended, cannot be stored each
   in a single contiguous block but become scattered across the
   file system.  This degrades performance as multiple seek
   operations are required to access a single fragmented file.

   Defragmenting consolidates each existing file and the free
   space into a continuous group of sectors.  Access speed will
   be improved due to reduced seeking.

   The rate of fragmentation depends on the algorithm used to
   allocate space and the number and position of free sectors.  A
   nearly-full file system will fragment more quickly.

   MS-DOS and Microsoft Windows use the simplest algorithm to
   allocate free clusters and so fragmentation occurs quickly.  A
   disk should be defragmented before fragmentation reaches 10%.

   See garbage collection.

   (1997-08-29)