A condenser microphone has a diaphragm separated by carbon that acts as a capacitor. A capacitor is a thing that stores electric energy. The condenser stores and releases the electronic signals when the diaphragm vibrates. In general it's a pretty sensitive mic that is primarily used for the voice.
The condenser microphone was invented by Edward Wente in 1916 as a much-needed low-noise substitute for the carbon microphone. It was basicly distortionless and became the standard microphone for acoustical measurements. It was then used in broadcasting for a few years, until replaced by the dynamic microphone, which is much easier to use but not actually "better".
Wente joined the Western Electric Engineering Department in 1914. his big project was a research gig focused on the design and calibration of a uniformly sensitive microphone for use in other sound research. The carbon micsthat already existed had too uneven a frequency response and too much background noise for sound research. Wente took a device known as an electrostatic transmitter (which was pretty useless) into the first flat frequency response microphone. He published his results in a Theoretical paper in The Physical Review the following year. In 1922, he produced a condenser transmitter with one hundred times greater sensitivity, which was enough to make it a practical device.
[That above mentioned electrostatic transmitter very old. Back in 1879 and 1881,Edison and Dolbear had introduced condenser transmitters. In 1900, Fessenden (probably) used one in his inaugural broadcast. ]
NOTE: In 1928 Georg Neumann started his microphone company in Berlin and began production of the CMV3 "Neumann Bottle" condenser mic. Neuman Co. claims to this day they invented the condenser mic. They didn't, they were at least 6 years too late. They did however make a pretty useful mic. In some literature they more specificly claim to have made the first metal diaphragm microphones... I am not sure if this is so. anyone?
There is a second type of Condenser mic, the electret microphone. It was invented at Bell laboratories in 1962 by Gerhard Sessler and Jim West. The Electret Mic unlike other condenser microphones, requires no polarizing voltage, instead containing an integrated preamplifier which usually takes phantom power.