A coverlet is a cloth spread over a bed as the top layer you see. It is usually quite thin and made to look nice, not to keep you very warm. Think of it as a decorative bed cover. It is not a blanket (which is for warmth), and it is not a duvet or comforter (which has filling inside). Though actually, in real homes people use the words loosely, and an old thin bedspread might get called a coverlet, a cover, or just the bedspread. The word sounds a little old-fashioned and bookish now; shops more often say bedspread or quilt. You still meet it in hotels, older houses, and stories.