A 
red dwarf is a small 
star on the 
main sequence, either late K or M 
spectral type. They have a diameter and mass of less than one-third that of the 
Sun (down to 0.08 solar masses, which are 
Brown dwarves) and a surface temperature of less than 3,500 K. They emit little light, sometimes as little as 1/10,000th that of the sun. Due to the slow rate at which they burn 
hydrogen red dwarves have a enormous lifespan, estimates range from a tens of billions up to trillions of years. Red dwarves never initiate 
helium fusion and so cannot become 
red giants, the stars slowly contract and heat up until all the hydrogen is consumed.  In any event, there has not been sufficient time since the 
big bang for red dwarfs to evolve off the main sequence.
Red dwarf stars are believed to be the most common star type in the universe. Proxima Centauri, the nearest star to the Sun is a red dwarf, (Type M5, magnitude 11.0) as are twenty of the next thirty nearest. 
See also: Stellar evolution,  Cataclysmic variable star, Hertzsprung-Russell diagram, Yerkes luminosity classification[?].
There is also a British 
science fiction/
comedy television series called 
Red Dwarf.
 
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