Docker gives developers the ability to package all their applications inside containers. These containers can run on any machine that has Docker installed and the application will be the same.
This is a great way to run a clone of a codebase on multiple systems and you can be sure that they are all going to be identical.
CI/CD workflows and DevOps testing environments are much better when using Docker which is essentially a set of software tools that can be shared.
Kubernetes is another tool used to operate multiple Docker containers, but on a much larger scale.