Software contianers (or Operating-system-level virtualization), is a computer virtualization method in which the kernel of an operating system allows the existence of multiple isolated user-space instances, instead of just one.
the best known example of this technology are Docker Containers.
Such instances, which are sometimes called containers, virtualization engines (VEs) or jails (FreeBSD jail or chroot jail), may look like real computers from the point of view of programs running in them - wikipedia 
On Unix-like operating systems, this technology can be seen as an advanced implementation of the standard chroot mechanism. In addition to isolation mechanisms, the kernel often provides resource-management features to limit the impact of one container's activities on other containers.
# See also - Operating-system-level virtualization - Docker - Docker Container