From LQWiki

/var is one of the key directories within a unix filesystem. It is designed as the storage area for 'variable' data within the Filesystem Hierarchy Standard.

A typical hierarchy under /var looks like:

account
cache
cvs
db
empty
ftp
games
gdm
lib
local
lock
log
mail -> spool/mail
nis
opt
preserve
run
spool
tmp
www
yp