An M Dwarf is a small M-Type Star. The term Red Dwarf includes M Dwarfs, but sometimes also includes small K-Type Stars (K Dwarfs). Early M Dwarfs (at the hotter end of the scale) are now considered likely places to observe Extra-Solar Planets within a Habitable Zone, one reason being M dwarfs are very common. But given their evolution, such planets are more likely to have experienced a longer period of stellar activity, giving it time to remove the planet's Atmosphere.
Brown Dwarf (BD)
M-Type Star (M)
Transiting Exoplanet Survey Satellite (TESS)
WFCAM Transit Survey (WTS)