Temp Sensor

An analog temperature sensor is a chip that tells you what the ambient temperature is. 

This one in particular is from Ada fruit that uses a solid-state technique to determine the temperature. It doesn't use mercury (like old thermometers), bimetalic strips (like in some home thermometers or stoves), nor do they use thermistors (temperature sensitive resistors). Instead, they use the fact as temperature increases, the voltage across a diode increases at a known rate.

https://learn.adafruit.com/tmp36-temperature-sensor/overview