In infrared photography, the film or image sensor used is sensitive to infrared light. Usually an “infrared filter” is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter therefore, looks black or deep red).
When a filter is used together with infrared-sensitive film or sensors, false-color or black-and-white images can result, with a dreamlike or somewhat ghostly/spooky appearance.