A Generic System Image (short GSI) is a android system image, which can be used to replace the existing installed android version with a new one (e.g. an updated one). Such an image is related to the project treble, which means, that the image can be installed on devices of different manufacturers without needing them to change hardware-specific implementations, as long as the device is treble enabled. The advantag is, that a GSI can, theoretically, be used on any treble-enable device. TO achieve this without treble, one would need to develop an own system image for each device that needs to be supported by the specific android version, which is way more time consuming.