Virtualization

Virtualization is Article description::the concept and technique that permits running software in an environment separate from a computer operating system.

The operating system actually running on the hardware is referred to as the host. On this host resides a hypervisor (aka virtual machine manager), which runs virtual machines containing guest software.

Containers
Containers provide isolated user space instances.

Orchestration
Container orchestration concerns the details of managing multiple Linux containers. This management layer spins up and spins down individual containers. Examples of container managers are Docker and Mesos, although others exist. There is also container orchestration where K8/docker swarm and related software compete for similar management functions.

Guest facilities
Most virtualization systems provide software to be installed inside the guest operating systems, to provide extra functionality.

These packages are for Gentoo guests running inside virtual machines. See respective hypervisor documentation for tools helping to run other operating systems inside virtual machines.