Container

Containerization is a form of Virtualization that happens on the Operating System (OS) level - hence it is also known as Operating-system-level virtualization. In containerization, the kernel of the OS allows the existence of isolated user-spaces. A user-space is a dedicated address space or region that allows for memory protection, in particular preventing a software from interfering with the kernels address space.

Sources: https://en.wikipedia.org/wiki/Operating-system-level_virtualization
https://en.wikipedia.org/wiki/User-space