/var/spool : Application spool data
Purpose
/var/spool contains data which is awaiting some kind of later processing. Data in /var/spool represents work to be done in the future (by a program, user, or administrator); often data is deleted after it has been processed. [43]
Specific Options
The following directories, or symbolic links to directories, must be in /var/spool, if the corresponding subsystem is installed:
/var/spool/lpd : Line-printer daemon print queues (optional)
Purpose
The lock file for lpd, lpd.lock, must be placed in /var/spool/lpd. It is suggested that the lock file for each printer be placed in the spool directory for that specific printer and named lock.
Specific Options
/var/spool/rwho : Rwhod files (optional)
Purpose
This directory holds the rwhod information for other systems on the local net.
Some BSD releases use /var/rwho for this data; given its historical location in /var/spool on other systems and its approximate fit to the definition of `spooled' data, this location was deemed more appropriate.