midnight commander

"mc" stands for midnight commander, which is itself a clone of Norton commander, which was sold by Symantec in the 80s and 90s. Norton commander was popular enough that by the time it was discontinued it had been ported to many other platforms (midnight commander being one of the ports for unix systems). Over time, Norton commander became the prototype for the "orthodox file manager", the category of file managers with two side-by-side file browser windows: many of the same key bindings for this category of file manager are the same as the original norton commander keybindings.

Midnight commander (and more generally an orthodox file manager) is especially useful for moving files from one system to another, as it usually supports browsing to remote file systems over ssh or ftp, and gives you a simultaneous view of where you're moving files from and to on the same screen.

The Wikipedia page is a pretty interesting read, actually: https://en.m.wikipedia.org/wiki/Midnight_Commander