K2-33 is a cool M-dwarf (about 0.56 solar masses, 3,540 K, 1.05 solar radii), 139 light-years from Earth. K2-33 b is a 3.70-Jupiter-mass companion, with an orbital period of 5.4 days, discovered in 2016 via transit. The inner world is a hot Jupiter — a gas giant hugging its star at a fraction of Mercury's distance — a class that forced astronomers to rethink how giant planets form and migrate inward. Repeated transit observations constrain the planet's orbital inclination and stellar density, anchoring the system's physical scale.