Shore power means plugging a vehicle, caravan or vessel into external mains electricity. In Australia, that usually means 240V AC from a powered site, marina, workshop or fleet depot.
The name comes from marine use: a boat at the dock connects to power from the shore instead of running its engine or draining batteries. The same idea applies to caravans, service vehicles and mobile workstations.
For an onboard battery system, shore power is a simple charging source. If the system has a built-in AC charger, the vehicle can be plugged in overnight and start the next day with a full battery.
Shore power is especially useful when vehicles return to a depot, workshop or home base. It reduces the amount of driving or solar input needed to stay charged.
If a power system can rely on shore power regularly, the overall system design may not need as much solar or battery reserve as a vehicle that parks remotely every night.