Bus Ripple
It is the voltage oscillation that the discontinuous switching current creates on the supply line. Its amplitude is determined by the capacitor value, its internal resistance and the inductance of the supply cable. For a correct measurement the probe must be connected directly to the driver's supply terminal, with a short lead.
The driver draws its supply current in pulses; these pulses create a voltage drop across the cable inductance and the capacitor's internal resistance. The result is that the supply voltage oscillates at the switching frequency. The amplitude can vary from a few hundred millivolts to a few volts.
The measurement point is critically important. In the same system you may measure 50 mV of ripple at the battery terminal and 1.5 V at the driver terminal; the difference is entirely the cable's contribution. For this reason, when evaluating ripple the measurement is always made at the driver input and with the shortest possible probe ground lead; a long crocodile-clip ground connection by itself shows oscillation that is not really there.
Large ripple has concrete consequences: an RF receiver and a controller sharing the same supply line see this oscillation as noise, and a system at the edge of its undervoltage lockout can shut down unnecessarily. The order of the solution is this: shorten the supply cable and increase its cross-section, tighten the connections, and if necessary add a capacitor at the driver input.
The context in which this term is used: DC Motor Driver Selection Guide