A few times now, the word 'Latest' has been seen around. For referencing Docker images we generally use Name:Tag, e.g. Node:8.11. If you don't specify a tag, either when creating a container or referencing one, it'll by default be latest.
For working locally, leaving things tagged as latest is fine, however once you get to sharing, purposefully tagging your images becomes very important.
Looking at the official Node images, (https://hub.docker.com/_/node/), they use tagging to specify a variety of options.
First they specify the runtime version, e.g. 8.12.0
Second they specify the underlying operating system, e.g. jessie, alpine or slim
jessie is a container optimised flavour of debian.
alpine is a super lightweight Linux kernel, that is used for size optimised images.
slim is a lighterweight version of jessie
Back in chapter one, we were saying that we got the benefits from containers by removing the operating system portion of a virtual machine. Now we're saying the you have to specify which operating system we want in the container.
In order to allow for applications to function in containers they still require a slimmed down kernel to function, although the majority of the syscalls are still passed through.