At its core, Docker provides a way to run almost any application securely
isolated in a container. The isolation and security allow you to run many
containers simultaneously on your host. The lightweight nature of containers,
which run without the extra load of a hypervisor, means you can get more out of
your hardware. Additionally, your application can always be packaged with its
dependencies and environment variables right in the build image, making testing
and deployment simpler than ever.