Freewheeling Diode (Motor Current Path)
A diode that provides a path for the inductive motor current to keep flowing when the switch turns off. Without this path, the sudden interruption of current would produce a spike of hundreds of volts according to V = L × di/dt and puncture the switch. It typically drops 0.7–1.2 V.
A motor winding is an inductance, and the defining property of an inductance is that its current cannot change instantly. When the PWM switch turns off, the current in the winding wants to keep flowing; the higher the resistance in its way, the higher the voltage that builds up across its terminals. If no path is provided, this voltage exceeds the switch's breakdown limit.
The freewheeling diode offers this current a low-voltage escape route and limits the spike to the supply voltage plus one diode drop. In an H-bridge this role is usually taken by the MOSFETs' body diodes; fast-recovery external Schottky diodes can also be added in parallel.
The same principle applies to relay coils. When you connect a relay to or next to the driver output, placing a reverse diode across the coil terminals prevents the spike generated at switch-off from damaging the driver electronics and the RF receiver. In the field, missing diodes on relays next to a motor driver are a known cause of unexplained lock-ups and fault complaints.
Context where this term is used: DC Motor Driver Selection Guide