WordNet (r) 3.0 (2006):

swap file
    n 1: the disk space that is set aside for virtual memory [syn:
         swap space, swap file]

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

swap file

    A file used by a program or, more often,
   an operating system as swap space.  A swap file is usually
   allocated as a long contiguous section of a hard disk to
   reduce access time.  The disk space used for a swap file can
   not be used for other things.  Under Microsoft Windows, swap
   files are recommended not to exceed three times the available
   RAM and are usually 150 percent of the RAM size.

   (1996-11-15)