An Ultraluminous Infrared Galaxy (ULIRG) is a Galaxy emitting more than 1012 times solar Luminosity in the Far Infrared. It can be considered a type of Luminous Infrared Galaxy, i.e., having 1011 times solar luminosity in far infrared. A Hyperluminous Infrared Galaxy is a galaxy with 1013 times solar luminosity in far infrared.
A LIRG is often a Starburst Galaxy and/or has an Active Galactic Nucleus or a Quasar. A ULIRG is typically a nearby galaxy (low Redshift), and often a Merger.