WordNet (r) 3.0 (2006):

Mb
    n 1: a unit of information equal to 1000 kilobits or 10^6
         (1,000,000) bits [syn: megabit, Mbit, Mb]
    2: a unit of information equal to 1000 kilobytes or 10^6
       (1,000,000) bytes [syn: megabyte, M, MB]
    3: a unit of information equal to 1024 kibibytes or 2^20
       (1,048,576) bytes [syn: megabyte, mebibyte, M, MB,
       MiB]
    4: (a British degree) a bachelor's degree in medicine [syn:
       Bachelor of Medicine, MB]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

MB
       MegaByte


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

MB
       MailBox


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

MB

    (Or "Mb") megabytes or megabits.  When referring to
   the size or data transfer rate of a storage device which is
   accessed in multiples of eight bits (e.g. RAM, hard disk)
   this almost certainly means megabytes, but when referring to
   the data transfer rate of a communications system it probably
   means megabits.  Some years ago, it is claimed, "MB" always
   meant megabytes and "Mb" meant megabits but recently this
   useful distinction has been lost.

   (1996-09-22)