spool file

from Jargon File (4.4.4, 14 Aug 2003)

spool file
 n.

   Any file to which data is {spool}ed to await the next stage of
   processing. Especially used in circumstances where spooling the data
   copes with a mismatch between speeds in two devices or pieces of
   software. For example, when you send mail under Unix, it's typically
   copied to a spool file to await a transport {demon}'s attentions. This
   is borderline techspeak.

from The Free On-line Dictionary of Computing (8 July 2008)

spool file

   Any file to which data is {spool}ed to await the next stage of
   processing.  Especially used in circumstances where spooling
   the data copes with a mismatch between speeds in two devices
   or pieces of software.  For example, when you send mail under
   Unix, it's typically copied to a spool file to await a
   transport {demon}'s attentions.

   [{Jargon File}]

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