Use for generic questions on containers that do not fall under a specific container technology, like Docker, LXC, FreeBSD Jails, OpenBSD sysjails, Solaris Containers, WPARs, etc. Also use where the specific technology is not relevant to the question.
Containers are Operating System level Virtualization technology. Where kernel of OS allows for the existence of multiple isolated user-space instances. Containers may appear as fully virtualize operating system, nevertheless they share kernel with the host OS and any issue affecting the kernel may equally affect all running containers.