This is the `yank-last-arg` readline comment. Bound to M-. and M-_ by default.
"Insert last argument to the previous command (the last word of the previous history entry). With a numeric argument, behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last word (or the word specified by the argument to the first call) of each line in turn."
Its sibling is `yank-nth-arg`, bound to M-C-y. So if you want the 2nd argument from the last command, you can press M-1 followed by M-C-y (yeah, arguments are indexed from 0)...
