Not an expert at all, but here's how I would simplify it. All corrections are welcome!
Docker has two main components. The daemon (you can think of it somewhat like a server) and the client (application you use to run commands).
When you install docker on your machine, it generally installs both. The daemon is a process that runs on your local machine and runs as root.
Rootless refers to the alternative method (used by podman for instance) to run the daemon as a standard user, and delegate root-level tasks to something else, like systemd for instance.
Docker has two main components. The daemon (you can think of it somewhat like a server) and the client (application you use to run commands).
When you install docker on your machine, it generally installs both. The daemon is a process that runs on your local machine and runs as root.
Rootless refers to the alternative method (used by podman for instance) to run the daemon as a standard user, and delegate root-level tasks to something else, like systemd for instance.