A planetary class for dry, generally inhospitable worlds, applied on screen to Tau Cygni V, the desert planet ceded to the Sheliak on which a forgotten human colony had nevertheless taken root.
Class H is one of the less often heard grades in the Federation's planetary classification. It denotes an arid world that is barely suited to humanoid life, a step further from the Earth-like norm than Class L.
The designation is used in The Next Generation episode The Ensigns of Command in 2366. Tau Cygni V is described as a Class H desert world bathed in hyperonic radiation, which ought to be fatal to humans, and under the Treaty of Armens it belongs to the Sheliak. The Enterprise-D learns that survivors of the colony ship Artemis adapted to the radiation and built a settlement of some fifteen thousand people there.
Because the radiation rules out transporters, Data is sent down alone to persuade the colonists to leave, while Picard searches the treaty for a way to hold the Sheliak off.