A system partition is the protected storage area on a device that contains core operating system files, startup components, and privileged applications. On Android and similar platforms, it is usually mounted read-only for normal use so everyday apps cannot alter it.
This matters because code placed in the system partition can run with higher trust than ordinary user apps. In attacks, threat actors may abuse firmware access or a compromised build process to plant malware, backdoors, or unwanted apps inside the system image. That can make removal difficult or impossible with a normal uninstall or factory reset. Defenders look for this risk by verifying firmware provenance, checking boot integrity, comparing signed system images, and auditing privileged packages that should not be present. In short, the system partition is a high-value target because control there can outlast user-level cleanup.