An endpoint OS is the operating system running on a user device, such as a thin client, laptop, or managed desktop, that connects to enterprise services. In VDI and DaaS environments, it is the local layer that handles login, device policy, session launch, and sometimes hardware access, even when the apps and desktops are hosted elsewhere.
This matters because the endpoint OS is part of the trust boundary. If an attacker gets local access, a weakness in the OS can lead to privilege escalation, policy bypass, or tampering with the device that brokers access to corporate resources. Defenders treat it as a security control point: keep images patched, remove stale versions, enforce least privilege, and monitor for unauthorized local accounts or elevated processes. A hardened backend does not help if the endpoint itself is compromised.