A submillimeter galaxy (SMG, or submillimeter-selected galaxy or dusty star-forming galaxy, i.e., DSFG) is a galaxy showing mostly through submillimeter radiation. These include high redshift galaxies. Specifically, the 850 μm flux density is generally greater than 3-5 millijanskys. They are very luminous because of star formation rather than because they are active galaxies. The spectrum typically seen is black-body radiation from dust grains and emission lines from the gas in the interstellar medium. Some have been estimated to have huge amounts of dust.
An SMG is typically a massive starburst high-redshifted elliptical galaxy. A SMG is essentially the same as a luminous infrared galaxy (LIRG). The phrase dusty galaxy is often used for them or to include them.