Phantom

Phantom is a term with multiple meanings. In general usage, a phantom is an apparition or ghost—an incorporeal being believed to be the spirit of a dead person or, more loosely, something perceived but not physically present. The word comes from Latin phantomem, via Greek phantasma, and is used as both a noun and an adjective to describe something illusory or unseen.

In medicine and science, phantom has precise uses. A phantom limb refers to sensations that an amputated limb still exists, sometimes with accompanying pain. In medical imaging, a phantom is an object with known properties used to calibrate and test devices such as CT, MRI, or ultrasound scanners. Anthropomorphic phantoms simulate human anatomy for protocol development and safety testing in radiation therapy and diagnostic imaging. The term also appears in psychology and perception to describe illusions or misperceptions.

In engineering and audio, phantom has practical applications. Phantom power is DC power sent through balanced audio cables to devices like condenser microphones, typically 48 volts. In electronics, phantom load or phantom power describes energy use from devices in standby or idle states. In databases, phantom reads refer to a phenomenon where a transaction reads rows inserted by another transaction, altering query results under certain isolation levels.

In culture, phantom is widely used in titles and character names. The Phantom of the Opera is a famous musical and novel figure, while The Phantom is a long-running comic-strip superhero. The term also appears in military designations, such as the F-4 Phantom II fighter jet. The word conveys elusiveness, mystery, and the unseen across its diverse uses.