What is the "map order" and "mapped window" in KWin?

I’m trying to understand changes in commit scripts/minimizeall: Try to preserve last active window · KDE/kwin@22b7ac0 · GitHub

The commit messages states:

Windows in workspace.clientList() are sorted in the map order. This
means that the minimize all script will try to activate the last mapped
window when unminimizing windows, which is a bit annoying.

What is the map order and mapped window?