Docker is a brand name for a bunch of totally unrelated concerns. It's some metadata attached to some tar archives. It's a repository that hosts said tar arch

Docker is a brand name for a bunch of totally unrelated concerns. It's some metadata attached to some tar archives. It's a repository that hosts said tar archives and metadata. It's a client for pushing and pulling said archives. It's a container runtime. It's a cgroups manager. It's a networking layer. It's a container orchestrator. It's a Mac app that requires you to pay them to run a Linux VM. They do a shit ton of stuff and named their product and their company the same thing, and were here pretty early on. My point is that it's a largely useless term. If you want to understand things at a deeper level, you have to cut through the cruft. You can put linux distributions into tar files and run them without Docker (see systemd-nspawn). You can use cgroups to run ordinary Linux binaries. You can make a group of processes run on a fake private network. You can build OCI-compliant container images without ever running a single thing in a container. Docker conflates all of this and confuses people. Don't be confused, realize that "Docker" does a lot.