Userspace is the part of an operating system where applications and many system services run. It is separated from the kernel by security boundaries such as process isolation, permissions, and sandboxing. In Android, most visible behavior comes from userspace components, including app processes and core services.
Userspace matters because a compromise here can still be serious, but it is usually less powerful than a kernel compromise. Attackers often exploit a userspace bug to get code execution in an app or service, then try to chain it with another flaw to escape the sandbox or gain higher privileges. Defenders focus on patching userspace services quickly, limiting privileges, and using isolation controls to keep a breach contained.