What is ir emitter, infrared emitter led, IR diode, detector circuit

 3 x 1.5 mm 60° 870 nm 20 mA Surface Mount Infrared Emitting Diode

https://www.futureelectronics.com/p/semiconductors--optoelectronics--infrared-emitters-detectors/hdn1102w-tr-stanley-electric-9066162