If you opt to use self-deployed sandboxes, they will be based on Docker. Docker is the leading cross-platform software container environment. Since this is a book about Dynamics 365 Business Central, this section will only be a quick introduction to Docker, but if you want to learn more, there are excellent learning resources in the official documentation by Docker (https://docs.docker.com/) and Microsoft (https://docs.microsoft.com/en-us/virtualization/windowscontainers/about/index), both of which are very good starting points.
Dynamics 365 Business Central runs only on Windows, so when you're looking for Docker documentation, make sure that it is intended for Windows. While most of Docker is platform-independent, there are some platform-specific sections as well.
In order to follow the content of the following sections, you need to know about the following...