The UL stands for "Underwriters Laboratory".  It used to be
	an Insurance Industry organization, but now it is independent
	and non-profit.  It tests electrical components and equipment
	for potential hazards.  When something is UL-listed, that means
	that the UL has tested the device, and it meets their requirements
	for safety - ie: fire or shock hazard.  It doesn't necessarily
	mean that the device actually does what it's supposed to, just
	that it probably won't kill you.

	The UL does not have power of law in the U.S. -- you are
	permitted to buy and install non-UL-listed devices.  However,
	insurance policies sometimes have clauses in them that will
	limit their liability in case of a claim made in response to
	the failure of a non-UL-listed device.  Furthermore, in
	many situations the NEC will require that a wiring component
	used for a specific purpose is UL-listed for that purpose.
	Indirectly, this means that certain parts of your wiring
	must be UL-listed before an inspector will approve it and/or
	occupancy permits issued.