Thermistors are special solid temperature
sensors that behave like temperature-sensitive electrical resistors. No surprise then that their name is a contraction of "thermal" and "resistor". There are basically two broad types,
NTC-Negative Temperature Coefficient, used mostly in temperature sensing and PTC-Positive
Temperature Coefficient, used mostly in electric current control.
There's even more history of the name and development of thermistors and facts about some key NTC parameters at the Kele
Electronics website, just be prepared for some strong opinions about one brand
of thermistor. They are mostly very small bits of special material that exhibit
more than just temperature sensitivity. They are highly-sensitive and have very
reproducible resistance Vs. temperature properties.
During the last 60 years or so, only ceramic materials (a mix of different metal oxides) was employed for production of NTC thermistors. In 2003, AdSem, Inc. (Palo Alto, CA) developed and started manufacturing of Si and Ge high temperature NTC thermistors with better performance than any ceramic NTC thermistors.
Thermistors, since they can be very small, are used inside many
other devices as temperature sensing and correction devices as well as in specialty
temperature sensing probes for commerce, science and industry. Some of those
new-fangled digital medical thermometers that get stuck in one's mouth by a nurse
with an electronic display in her other hand are based on thermistor sensors.
They are probably inside your cell phone, automobile, stereo and television, too,
but you'd never know it unless you were an engineer or visited here. Thermistors
typically work over a relatively small temperature range, compared to other temperature
sensors, and can be very accurate and precise within that range, although not
all are. | 
