Circulator – A 3-port, non-linear device that directs signal flow around a circle, from port #1 to port #2, from port #2 to port #3 and from port #3 to Port #1.
Isolator – A 2-port device that allows signal flow in one direction and absorbs signal flow in the reverse direction.
Microwave – A portion of the electromagnetic spectrum generally considered to cover the range from 1 GHz to 30 GHz, but sometimes used to refer to a broader range from around 0.5 GHz to 100 GHz and even beyond. Not hard and fast definition.
Millimeter-wave – (also written MMW, mm-wave) – A part of the electromagnetic spectrum covering roughly 50 GHz to about 1 THz (1000 GHz). The wavelength in free space is 1 mm at 300 GHz, thus the term.