What is Docker and how does it differ from virtual machines?

Docker is a containerization platform that packages applications and their dependencies into lightweight, portable containers. Key differences from VMs: 1) Architecture: Docker containers share the host OS kernel, while VMs have their own OS, 2) Resource Usage: Containers are more lightweight and use fewer resources, 3) Startup Time: Containers start in seconds, VMs take minutes, 4) Isolation: VMs provide stronger isolation, containers provide process-level isolation, 5) Portability: Containers are more portable across different environments. Example: A Docker container might use 50MB RAM, while a VM for the same application could use 1GB+.