What is Docker

Docker is advanced version of virtualization that use OS-level virtualization or (containerization) and deliver software in packages called containers.

Docker is a Platform as a service(PAAS) which is an open source and designed to create, run and deploy applications.

Docker is written in ‘GO’ language and rely on host Operating System to run applications. It do not contain any virtual Operating System. However it possess O.S who takes less space in memory because of few files within it. Due to this, we can even neglect its presence.
Suppose we want to run Linux OS in container then Docker engine firstly look up in host machine OS files and process them. Then gather the pending files from Docker Hub.