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

cache line
cache block

    (Or cache block) The smallest unit of memory than
   can be transferred between the main memory and the cache.

   Rather than reading a single word or byte from main memory at
   a time, each cache entry is usually holds a certain number of
   words, known as a "cache line" or "cache block" and a whole
   line is read and cached at once.  This takes advantage of the
   principle of locality of reference: if one location is read
   then nearby locations (particularly following locations) are
   likely to be read soon afterward.  It can also take advantage
   of page-mode DRAM which allows faster access to
   consecutive locations.

   (1997-01-21)