Icy ocean worlds with ice-covered seas covering more than 85% of the planet's surface. These are Pelagic worlds with their crusts frozen over due to a variety of reasons, most often a lack of greenhouse gas in the atmosphere.
Tidal or subsurface geological stresses often create cracks in the global ice coverage, allowing a thin atmosphere of oxygen and nitrogen to form. Were it not for constant replenishment from these rifts, the atmosphere would desiccate within a few million years. However carbon dioxide may build up in the atmosphere over time, emitted from suboceanic volcanoes, allowing the oceans to melt temporarily or permanently.
PelaGeligian worlds can often be successfully terraformed by artificial heating, either by increasing the amount of incident sunlight, or by increasing the greenhouse gas content off the atmosphere.