New for October 2016!
Maser is an acronym of microwave amplification by stimulated emission of radiation. Masers predate lasers by several years, and the original maser was developed by Charles Townes at Columbia University and first demonstrated in 1953 with an output near 24 GHz. The original term for "laser" was "optical-maser" by the way, and the first laser was demonstrated in 1960. Charles Townes is a member of our Microwave Hall of Fame.
Hydrogen masers provide a very stable signal at 1,420,405,752 Hertz, so stable it is used in atomic clocks.
Here's recent video explaining solid state maser which does not require cryo-cooling, a very recent development. People involved in masers can be referred to as "the maserati".
Room-Temperature Solid State Maser by Dr. Mark Oxborrow at Imperial College