In general:
Summary of all processes that convert a weak input signal into a greatly amplified, proportional (power amplification).
In fluid technology:
Servo technology stands for an area that uses a power amplifier and a feedback (i.e. a ) to change a (mechanical) output variable to a defined factor of what is normally a very weak input signal. The signal processing may be mechanical (e.g. copying) or electrical (electronic). This field is more accurately named electro-hydraulic control technology.