spool file n.

Any file to which data is spooled 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.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.