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

fully associative cache

    A type of cache in which data from any
   address can be stored in any cache location.  The whole address
   must be used as the tag (the value that identifies a block of data
   in the cache).  All tags must be compared simultaneously
   (associatively) with the requested address and if one matches then
   its associated data is accessed.  This requires an associative
   memory to hold the tags which makes this form of cache more
   expensive.  It does however solve the problem of contention for
   cache locations (cache conflict) since a block need only be
   flushed when the whole cache is full and then the block to flush
   can be selected in a more efficient way.

   The alternatives are direct mapped cache or set associative
   cache.

   (2013-08-09)