What is an instrumentation amplifier and why is it preferred for sensor interfaces?

An instrumentation amplifier is a precision differential amplifier with three op-amps providing high input impedance on both inputs, high CMRR (>100dB), adjustable gain with single resistor, and low offset drift. The standard topology uses two input buffers and one differential stage. It is preferred for sensors because it can accurately amplify small differential signals (mV range from strain gauges, thermocouples) while rejecting large common-mode signals from ground loops and interference.