A man-month is a hypothetical unit of work denoting the amount of work a man can theoretically do in a month's time.

This is fuzzy to being with and Fred Brooks argues in The Mythical Man Month, his book, that it is a myth that paths to success may be gauged with this junk metric in a helpful way. This is not the main takeaway from the book, but instead I mention it as I wondered today what the name meant.