Class M refers to a classification of planets that are capable of supporting human life. These planets typically have a suitable atmosphere, temperature, and water sources, making them ideal for habitation. The term is often used in science fiction, particularly in the Star Trek universe, to describe worlds that resemble Earth. In the Star Trek series, Class M planets are explored by starships and serve as potential locations for colonization or research. These planets usually feature diverse ecosystems and can sustain various forms of life, including humans. The classification helps in identifying habitable environments in the vastness of space.