Docker is an open-source platform using which a developer can build, package, and distribute any application as a lightweight container. A container is nothing but an isolated self-sufficient environment.
With docker, developing an application locally has become easier. If you have to work with multiple different frameworks or versions of any programming language, you can create separate containers, build your apps, test everything inside different containers, and then destroy them.
Another use of docker is in the distribution of applications. When you develop an application you set everything that is required by the application in your local environment, but what if some dependencies are missing in the production environment? This situation is handled by docker, as you can dockerize an application along with its runtime environment and dependencies by creating a docker image, and then that docker image can be used to start a container and run the application inside it.
Docker has made software deployment super easy, and with Docker, you can move applications between development, testing, and production environments without losing your sleep.