Docker is a technology where developers or DevOps teams can build, deploy, and manage applications by using containers. Docker is an open source software so that everyone can run this on their own operating system, which should support virtualization and Docker for Mac/Windows/Linux.
Docker also ships the ready images from one computer to another. Docker containers are sets of processes that are isolated from the rest of the processes in the host OS. Docker shares the kernel of the host operating system. On the other hand, VM is a technology that depends on the guest OS, which is completely separated from the host OS. Virtual machines communicate with the host OS through hypervisor. VM requires many hardware resources and processes. It's not a container-based technology.