A Kubernetes node is the host machine, physical or virtual, that runs containerized workloads in a cluster. Nodes provide the operating system, container runtime, networking, and kernel features that pods depend on to execute.
Nodes matter in cyber security because compromise at this layer can undermine everything running on top of it. If an attacker gains root on a node, they may inspect processes, tamper with cgroup or filesystem data, alter runtime state, or interfere with workload attestation. That can weaken defenses that rely on the node to honestly report what workload is present and can even support identity impersonation in systems such as SPIFFE and SPIRE. For defenders, node hardening, patching, least privilege, and strong attestation integrity are essential, because workload identity is only as trustworthy as the host that vouches for it.