Docker is a virtualization software under the category of Platform as a Service (PaaS) products. It virtualizes operating systems in lightweight and portable packages called containers. Containers are lightweight virtual machines that are uses the parent OS kernel. They are isolated and have their own configurations and dependency, though they may communicate with other containers through defined communication pipeline.
This is a companion discussion topic for the original entry at http://iq.opengenus.org/basics-of-using-docker/