The expression is used to refer to lazy, useless people. The Korean translation would be "아무것도 안 하고 (無爲) 먹기만 한다 (徒食)."無爲徒食Do nothing (無爲), but (徒) eat (食).
When I saw the expression today, I already knew it, including the meanings of all the characters. It literally means "Nothing (無) do (爲), only (徒) eat (食)." So why am I posting about it? Because when I saw the 徒 (도) in the expression, I suddenly remembered a post I did a couple of months ago, in which I expressed my surprise that the character 從 (종) could also mean "only." I thought I had seen it translated as "only" in "Du's Handbook of Classical Chinese Grammar," but when I saw this old saying today, I realized I had probably confused a 徒 (도) in "Du's Handbook" for 從 (종). And, sure enough, today when I checked the sentence in "Du's Handbook," the character in the sentence was 徒 (도), not 從 (종), two very similar-looking characters.
It was a stupid mistake, so now I will have to delete the post to avoid confusing people. Sorry!