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

soft boot
 n.

    See boot.


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

soft boot

    A boot which resets only part of the
   system.

   For example, "If you're running the mess-dos emulator,
   control-alt-insert will cause a soft boot of the emulator,
   while leaving the rest of the system running".

   Contrast hard boot.

   [Jargon File]

   (1995-11-27)