When we refer to containers, we almost always mean Docker containers (https://www.docker.com/). Docker is the most popular software tool for running programs in containers, which are isolated environments.

Containerization is a kind of virtualization where the scope of the application's resources is limited. This means the application works at its maximum performance level. This is different from full virtualization, where you have to run the full operating system with the corresponding overhead and run your application inside that isolated operating system.

Docker has become popular for a variety of reasons. One of these reasons is that it has a registry—the place where you can upload and download images of containers with applications. The public registry is Docker Hub (https://hub.docker.com/explore/), but you can have a private registry for a private or permissioned software.