Docker is an open-source platform that simplifies the process of developing, deploying, and running applications using containerization. Unlike traditional virtual machines, Docker containers share the same operating system kernel, making them lightweight and efficient. Each container packages an application along with its dependencies, ensuring consistent performance across different environments. This isolation allows developers to create, test, and deploy applications seamlessly, regardless of the underlying infrastructure. Docker is widely used in DevOps practices, enabling rapid application delivery and scalability, making it a vital tool in modern software development and deployment workflows.