Docker is a containerization platform that packages applications and their dependencies into lightweight, portable containers. Unlike virtual machines that virtualize entire operating systems, Docker containers share the host OS kernel while maintaining application isolation.
Key differences:

• Resource Usage: Containers use fewer resources as they share the host kernel
• Startup Time: Containers start in seconds vs minutes for VMs
• Portability: Containers run consistently across different environments
• Isolation: VMs provide stronger isolation but at higher overhead cost