1. Something apparently seen, heard, or sensed, but having no physical reality; a ghost or an apparition.
2. Something which is elusive or delusive.
3. An image that appears only in the mind; an illusion.
4. Something dreaded or despised.
5. Of, or related to, a nonexistent source of sensation; applied specifically to a bodily limb that has been amputated, but is the apparent source of pain; such as, a phantom limb.
6. A collection of materials used to simulate human tissue in testing radiation absorption and backscattering.
7. A term for a volume of material approximating as closely as possible the density and effective atomic number of living tissue, used in biological experiments involving radiation.

A circuit that originates from center taps on two side circuits, with no additional wire lines.

Continuous electricity use by appliances, television sets, computers, and other such devices even when they are ostensibly not operating; such as, a computer or printer in "sleep" mode.

Also called a phantom transaction or false read.

This takes place when a reader reports the presence of a tag that doesn't exist.

Signals of unknown origin appearing on a radar screen that do not correspond to the target; generally the cause is unknown, although they may result from faulty circuitry, interference, or jamming.