Grid interactive refers to the interaction with the grid by means of AC current. This system can feed to and from the grid to feed the loads. The system can also feed from batteries and too batteries when required as well as feed power from solar directly to the loads bypassing the batteries and the grid.
This is the most flexible way to work a solar installation.
A system can be run off grid with Eskom as a backup to the solar system in the event of bad weather. If there is excess power once the batteries have been charged and the loads supplied, then this power can be fed back to the grid.
Some grid interactive inverters do not feed to the grid but only from the grid and are usually called bi directional inverters.
A generator can also be connected to the inverter as the second source of power if Eskom is not available or in the semi off grid scenario.