What does the idiom “three sheets in the wind” mean and Where does it come from?

The expression “three sheets in the wind” means, of course, pretty drunk, reeling from too much indulgence in strong drink, somewhat more tipsy than “half-seas over.”

Like many other common expressions, the phrase dates back to the times when ocean navigation was entirely by sail.

But in nautical use, a sheet is not a sail, as landsmen are accustomed to suppose, but the rope or chain attached to the lower corner of a sail by which the angle of the sail is controlled. In a strong wind the sheet may be loosened, and is then said to be “in the wind,” flapping and fluttering without restraint.

If all three sheets are loose, as in a gale, the vessel staggers and reels very much like a drunken person.