Gas Dwarf

A Gas Dwarf (also known as a Mini-Neptune, if it is similar in composition to an ice giant rather than a gas giant) is a planet of similar composition and density to a giant planet, but has a much smaller mass (usually under 10 M⊕). The relationship between mass and radius of a gas dwarf is not exactly the same as that for gas and ice giants, and can change vastly with stellar irradiation, perhaps even allowing the dwarf to become as big as regular giant planets.

Gas dwarfs lose their atmospheres to hydrodynamic escape more quickly, and thus will only be found in the outer regions of a planetary system.

Worldbuilding in Practice
"Galt is a tiny class I gas dwarf orbiting Ascott at a distant 21.3 AU. It has a mass of roughly 6.5 M⊕, most of which is a 5 M⊕ core, and a radius of 3.8 R⊕. Despite a paucity of moons (Galt has only 3 major moons and a number of small asteroid moons) and being relatively difficult to access from Dagny, it is nevertheless heavily developed, as it is the only viable giant planet in the system."