Endpoint posture is the current security state of a device used to access systems. It usually includes whether the device is compliant with policy, whether patches and antivirus are current, whether disk encryption is enabled, and whether risk indicators suggest compromise.
It matters because many access systems no longer trust a username alone. VPNs, zero-trust gateways, and conditional access tools can check endpoint posture before allowing login or opening an application. A healthy laptop may be allowed full access, while an unpatched or jailbroken device may be blocked, quarantined, or limited to a safer path. In attacks, stolen credentials are often paired with a compromised endpoint to bypass basic authentication. In defense, posture checks help reduce blast radius by stopping risky devices early and by giving security teams a signal that something has changed on the host.