What is Docker?

Docker is an open-source platform for automation that enables developers to create, deploy, and run applications in containers. This technology allows developers to package applications along with their dependencies into standardized units called containers. These containers can run consistently on any system that has Docker installed, regardless of the underlying infrastructure, which significantly improves the process of deployment and scaling applications.

Using Docker, development teams can ensure that their applications behave the same way in development, testing, and production environments because containers encapsulate all the necessary components. This leads to more efficient workflows and a reduction in the "it works on my machine" problem, as the environment within a Docker container remains unchanged across different stages or systems.

The other options don't align with the core functionalities of Docker: it is not a cloud storage service, it is not a programming language, and while it can work with web server software, it is not web server software itself. Docker's primary value lies in its capability to facilitate containerization and automate application deployment, making it a vital tool in modern software development practices.