Photography using light above 720nm or thereabouts. Several companies can modify existing consumer level equipment to use this range natively, or to accept all light, thereby requiring a lens-filter to limit to the desired wavelengths.
Infrared photography tends to produce an eery appearance, in part because plant life appears very bright (white), and clouds in the sky stand out much more so than in visible light.
 "Alewife IR (2011)")