In astronomy (Far-Infrared Astronomy), the term is typically used for the wavelength range is 30-450um. It can indicate cold clouds of gas and Dust, cold matter of 140 Kelvins or less. The term Submillimeter Astronomy covers the range from 450um to 1mm and perhaps sometimes is used to cover far infrared astronomy as well.
Cosmic Background Explorer (COBE)
Herschel Space Observatory
Hyperluminous Infrared Galaxy (HLIRG)
James Clerk Maxwell Telescope (JCMT)
Luminous Infrared Galaxy (LIRG)
Submillimeter Telescope (SMT)
Ultraluminous Infrared Galaxy (ULIRG)