What is a spool file?
A spool file is a file containing a job destined for a specific printer. When you print a file, the application you use to print writes a file to the spool folder for that printer. The system monitors this folder. When a file appears in the folder, it sends that file to the printer, and deletes it from the spool folder.
It is common to use a spool file as the sample data file for a document you intend to install on a printer.