Docker
In a nutshell, docker executes containers, which is a customize instance of a
docker image. An image is all the instructions to encapsulate libraries,
dependencies, environment variables, configuration... in a file called
Dockerfile to enable easy initialization of new services, without install any
local dependencies that can corrupt your system. It is like a virtual machine,
but with the difference of you can type out from commands line and it is not a
full OS, just the necessary to run the service.
As images are reusable by team or the community, they are stored in a container image registry, which is a place to store images. Docker hub is the most popular, but for self-hosted, Artifactory or quay.
After image is build, you can then start multiple containers of the same image, which are independent and can run in parallel.
You can start/stop/access those containers. Totally portable to any OS.