Docker is a platform for developing, shipping, and running applications inside containers. It provides tools and an ecosystem for creating, managing, and deploying containers that package an application and its dependencies into a single, portable unit. Docker containers are lightweight, fast, and consistent across different environments, making it easier to develop, test, and deploy applications. Docker also includes features for managing containerized applications, such as Docker Compose for defining multi-container applications and Docker Swarm for orchestrating clusters of Docker engines. Docker has become a fundamental technology in modern DevOps practices, enabling greater efficiency, flexibility, and scalability in software development and operations. Its widespread adoption has led to a robust community and ecosystem, further driving innovation and best practices in containerization.