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

Nibble Mode DRAM

    A standard DRAM where four successive bits can
   be clocked out of the single data line by successive pulses on
   the CAS\ line while RAS\ is active.  A column address is only
   required for the first bit.

   This mode is now unfashionable but can be found on some older
   64 kilobit and 256 kilobit chips.

   (1997-12-03)