Current Sharing
It describes how the total current is distributed among power switches connected in parallel. The distribution is inversely proportional to the channel resistances and is never exactly equal; the fact that MOSFET channel resistance rises with temperature heats the device drawing more current and shifts current to its neighbour, providing natural balancing.
If one of two parallel MOSFETs is 8 mΩ and the other 12 mΩ, the current splits roughly 60 to 40. The device drawing more current heats up more, its resistance rises as it heats, and the share re-balances. This positive temperature coefficient is the property that makes paralleling MOSFETs far safer than paralleling bipolar transistors.
For the balancing to work it is an advantage that the devices are thermally coupled, that is, sit on the same heatsink. In devices that are isolated from each other and run at different temperatures, the balancing weakens.
The same concept also applies outside the driver. When you connect two motors in parallel to a single driver, the current does not split equally; the motor with the greater mechanical load draws more current. That is why, when using parallel motors, the driver must be selected according to the total worst-case current of the two motors, and the starting surges must also be evaluated over that total.
Context where this term is used: DC Motor Driver Selection Guide