Switching Loss
It is the power loss arising from current and voltage both being non-zero at the same time during the transitions when the switch turns on and off. A fixed amount of energy is spent at each transition; therefore the total loss grows in direct proportion to the switching frequency. Doubling the frequency doubles this component too.
When a MOSFET is fully off there is voltage across it but no current; when fully on there is current but almost no voltage. The loss in both states is small. The loss arises during the transition, on the order of hundreds of nanoseconds: while the voltage is still falling the current rises, and the product of the two can momentarily reach hundreds of watts.
Because this energy is repeated at every transition, the total loss is expressed as E × f. A switch spending 20 µJ per transition produces 0.4 W at 20 kHz and 2 W at 100 kHz. Unlike conduction loss, this component is not proportional to the square of the current but roughly proportional to the current, and it also grows with the supply voltage.
The practical consequence is this: a high switching frequency removes motor hum and lowers the current ripple, but heats the driver. In 12–24 V DC drivers the 16–25 kHz range is typically taken as the region balancing these two wishes. If your driver is heating up unexpectedly, you need to think about the frequency side as much as the current consumption.
Context where this term is used: DC Motor Driver Selection Guide