Docker is an open platform for developing, shipping, and running applications. Docker can bundle up an application and its dependencies in a virtual container that can run on any operating system like Linux, Windows, and macOS. This allows the app to run in various locations, such as on-premises, a public cloud, and/or a private cloud.

A Docker Container follows a similar logic like a virtual machine, however, it doesn’t have any operating system installed and running on it. Hence, containers are lightweight and don’t require much space and resources on your machine, which is why you can run multiple containers simultaneously. Containers are isolated from each other, but you can establish a connection between them. Docker containers are standardized, lightweight, and secure.

A Virtual Machine, in a nutshell, is a computer that runs inside a computer. The program controlling virtual machines is named a hypervisor and the computer in which the virtual machine is running called the host. Virtual machines and host machines are also completely isolated. Therefore, if your virtual machine crashes, it won’t affect your host machine in any way. However, compared to containers, virtual machines have operating systems installed, so they require a lot of space and resources on your computer. That's why your computer can't host and run many virtual machines at the same time.

In conclusion, Docker allows you to separate your applications from your infrastructure so your application can run uniformly in developing, testing, or staging environments. By using Docker you can significantly decrease the time between writing code and running it in production.