A mount namespace is a Linux kernel feature that gives a process its own view of mounted filesystems. Inside one namespace, a process may see different mount points, bind mounts, or filesystem roots than processes in another namespace, even though they share the same host kernel. This is a core building block for containers and snap confinement, because it helps separate what an app can see from what exists on the host.
In security terms, mount namespaces reduce the blast radius of a compromise by hiding or remapping sensitive paths. Defenders use them to isolate application files, restrict access to host data, and create cleaner sandbox boundaries. Attackers, on the other hand, often target the privileged helper that creates or configures the namespace; if that code is flawed, a local user may gain visibility into host mounts or interfere with confinement before the app starts. For that reason, mount namespaces are only as strong as the code and permissions that set them up.