jargon.artrocity.com
New Hacker's Dictionary the Jargon File v 4.4.6
[Cisco] A command in a complex piece of software which is more likely to be used by an extremely experienced user to tweak a setting of one sort or another - a setting which the average user may not even know exists. Nerd knobs tend to be toggles, turning on or off a particular, specific, narrowly defined behavior. Special case of knobs.