The warm gas dwarf Kepler 11f compared in size to Earth
Gas dwarfs are worlds with thick, helium-rich atmospheres and small, low density cores depleted in ices and rock. Gas Dwarfs are smaller than Microjovian gas worlds, which have a lower limit of 0.08 x the mass of Jupiter (24 x the mass of Earth), and can be distinguished from Panthalassic worlds of similar mass by their relatively low density and deficiency in ices.
These planets are commonly known as Gas Dwarfs, but are classified as Nebulous Superterrestrials in the NolWocs system. Kepler 11-f was the first such planet ever discovered, 2000 ly from Sol in the Cygexpa volume. Although Gas Dwarfs often retain a substantial amount of hydrogen in their atmosphere, this will tend to bleed off over time by the mechanism of Jeans escape, a process which is highly dependent on temperature.
Helium worlds of this kind often have super-rotating atmospheres; those which are tidally locked often have wildly asymmetric weather patterns. An example of this type of world is Fira in the Oia system.