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

BRS
       Big Red Switch


The Jargon File (version 4.4.7, 29 Dec 2003):

BRS
 /B?R?S/, n.

    Syn. Big Red Switch. This abbreviation is fairly common on-line.


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

Big Red Switch
BRS

    (BRS) IBM jargon for the power switch on a computer,
   especially the "Emergency Pull" switch on an IBM mainframe or
   the power switch on an IBM PC where it really is large and red.

   "This !@%$% bitty box is hung again; time to hit the Big Red
   Switch."

   It is alleged that the emergency pull switch on an IBM 360/91
   actually fired a non-conducting bolt into the main power feed; the
   BRSes on more recent mainframes physically drop a block into place
   so that they can't be pushed back in.  People get fired for
   pulling them, especially inappropriately (see also molly-guard).

   Compare power cycle, three-finger salute, 120 reset; see
   also scram switch.

   [Jargon File]

   (2014-08-10)