Container isolation is the security boundary that separates processes running in a container from the host and from other containers. It is usually built with kernel features such as namespaces, cgroups, and capability limits, which make workloads look separate even though they share the same underlying operating system.
In cyber security, isolation matters because it limits blast radius. If an attacker gets command execution inside a container, strong isolation can prevent easy access to the host, credentials, or adjacent services. But isolation is not a complete defense: weak configuration, mounted secrets, broad network access, or excessive privileges can turn a container compromise into a larger incident. Defenders harden containers by removing unnecessary capabilities, running as non-root, restricting egress, and applying least privilege to files, sockets, and APIs.