A "defrag token" is a fictitious license or currency required to execute the windows "Defrag" program. The token does not exist, but can be used to help limit a (l)user's defragging in futile attempts to improve the performance of their system.
It has a secondary effect of pre-flagging unwary users for the IT support staff -- similar to the purpose of a left-handed ethernet cable.
(l)user: my computer is slow, I'm gonna run "defrag" a few times to fix it.
BOFH: k, but you better stock up on defrag tokens
(l)user: good idea!
(l)user (to helpdesk): I need a bunch of defrag tokens, I'm saving you guys lots of time