Docker is a platform for running and managing Linux containers that provides lightweight virtualization compared to traditional virtual machines. It allows applications to be packaged into standardized units called containers that have all their dependencies and can be run on any infrastructure that supports Docker. Docker improves deployment by allowing applications to be easily moved between development, testing, and production environments using self-contained images. As Docker grows in popularity, companies like Red Hat are integrating it into their middleware products and looking to distribute software via Docker containers and images.