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

BogoMIPS
 /bo'go?mips/, n.

    The number of million times a second a processor can do absolutely nothing.
    The Linux OS measures BogoMIPS at startup in order to calibrate some soft
    timing loops that will be used later on; details at the BogoMIPS mini-HOWTO
    . The name Linus chose, of course, is an ironic comment on the uselessness
    of all other MIPS figures.


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

BogoMips

    (From "bogus", "MIPS") The timing unit of the Linux
   kernel.

   A BogoMips is an unscientific measurement of processor speed
   made by the Linux kernel when it boots, to calibrate an
   internal busy-loop.

   BogoMips MiniHowto
   (http://metalab.unc.edu/LDP/HOWTO/mini/BogoMips.html).

   (1999-05-06)