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

ABR
       Available Bit Rate (ATM, CBR, VBR, UBR, QOS, BIT)


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

automatic baud rate detection
ABR
autobaud

    (ABR, autobaud) A process by which a
   receiving device determines the speed, code level, and stop
   bits of incoming data by examining the first character,
   usually a preselected sign-on character.  ABR allows the
   receiving device to accept data from a variety of transmitting
   devices operating at different speeds without needing to
   establish data rates in advance.

   (1996-06-18)