Docker is an open-source platform that enables developers to automate the deployment of applications in lightweight, portable containers. These containers bundle the application code along with its dependencies, ensuring consistency across environments. Docker simplifies application scaling, deployment, and version control, making it a key tool in DevOps workflows. It is widely used for microservices architectures, CI/CD pipelines, and cloud-native development. Docker's ability to isolate applications improves security and resource efficiency.