A length of fabric, usually triangular, worn around the neck and shoulders. Sometimes tucked inside the neckline of the bodice, sometimes crossed over the bodice. See the image at right in which all three women are wearing fichus of the late 18th century type. This “pouter pigeon” style of fichu fell out of fashion during the Regency years, though the term was resurrected c.1816 to refer to various sorts of bodice tuckers.
The print shows a detail of "Morning Dresses" from The Gallery of Fashion, July 1794.