The ratio of an input and an output (gain). The value is used to adjust reactions (responses) or deviations when a controller controls a servo motor. In servo motors, the ratio works as a parameter to decide responses or stability of movement. There are speed loop gain and position loop gain etc. Generally, to make servo gain higher causes better response and less bias.
But when it is too high, vibration (resonance phenomenon) occurs.
A gantry with X-Y axes and a guide to support the Y axis so that the axis can carry a heavy load.