Early in the period known as the French Second Empire “sleeper” earrings were comprised of a single diamond, and were the only earrings worn. The fashion for hairstyles consisting of heavy coils wound around the head and bonnets surrounding the face, sporting flowing ribbons, completely camouflaged the earlobes. 

Eventually, hairstyles evolved, ringlets replaced heavy coils, and face-framing bonnets disappeared. Earrings reappeared c.1860 when earlobes again were available to suspend all manner of incredible designs, in many cases the longer the better.¹

In contemporary parlance, a sleeper earring is a golden hoop earring of simple design and is used to keep the piercing in the earlobe open.

Source

• Vever, Henri, Purcell, Katherine (translator). French Jewelry of the Nineteenth Century. Paris, France: H. Floury, 1906-1908 – Reprinted: London: Thames & Hudson, Ltd., 2001.