So now that Windows server 2016 is generally avalible for the first time ever windows users can now use containers. Ok, so what exactly are containers? Well more or less they are virtual operating systems that share the same kernel as the host OS. In regular VM's the hardware is shared between machines, but containers go a step further and share the kernel of the OS. Why does this matter? Well because you are sharing an existing kernel that is already running, your startup times are instantanious. To put this in perspective, this is virtualization at the OS level.
On Linux, containers have been a thing for a long time. This technology is called LXC. Docker itself is a layer ontop of various container platforms embedded in operating systems.