Docker is a free and open-source tool that uses OS-level virtualization to deliver software in packages called containers. Docker is specially designed to make it easier to create, deploy and run applications by using containers. Docker containers are lightweight and very similar to Virtual Machine, using the host OS. Containers allow you to package up an application with all required libraries and other dependencies and ship it in one package.
Docker shares the same Linux kernel and other resources as the system that they’re running on, and only require the application along with its dependencies to be packaged. This will speed up your system performance and reduces the size of the application. Docker is free, so anyone can contribute to Docker and it being open-source allows anyone to extend it and meet their own needs. The main goal for the Docker is for developers to develop the applications easily, ship them into containers, and deploy it anywhere.