Docker is an open-source platform that allows for creating, deploying, and running applications in containers. Containers are lightweight, isolated environments that encapsulate an application and its dependencies, ensuring consistency and portability across different environments. Docker simplifies the process of packaging and distributing applications, as containers can be easily deployed on any system with Docker installed. It provides an efficient way to manage and scale applications, offering flexibility, resource optimization, and reproducibility. Docker has gained significant popularity in software development and deployment, revolutionizing the way applications are built, shipped, and run.