Angel sleeves are a style of sleeve that dates back at least to the Renaissance. Instead of being fitted to the arm, the sleeves are cut with lots of extra material, so that they have the appearance of "wings." The exact length of the angel sleeves varies widely, from just below the elbow to covering the hands, and the extra material might be so long that it trails on the floor.
Though many angel sleeves are cut very long, so that the open cuffs reach down to the knee, the term can be used as a general name for any sleeve that is made with a lot of material and doesn't have a gathered cuff. For example, kimono sleeves have a similar construction can be referred to as angel sleeves. In some cases, the term "angel sleeves" may refer to any kind of ruffle of material that sits on the shoulder like a tiny angel's wing.
There are several ways to make angel sleeves for a garment. Such sleeves can be used to make an angel wing dress or an angel sleeve bodice. One way is to cut a large circle of cloth and fold it in half. A circle is cut in the center of the cloth, making an armhole that will then be attached to the shoulder of the garment. The excess material creates a large, unfitted, flowing sleeve.
Another way of creating an angel sleeve involves cutting out a large rectangle of cloth and folding it widthwise, with one end of the folded rectangle being gathered to fit it to the shoulder of the garment. The sides of the rectangle are sewn together, and the material at the cuff isn't gathered, but allowed to hang free. This last detail is what mainly differentiates an angel sleeve from other types of sleeve that also require a great deal of material to make.
Even though angel sleeves mainly went out of fashion with the Middle Ages, they can still be seen on some women's and men's clothing today. Many academic robes worn by college graduates have angel sleeves. So do several kinds of Halloween costumes, such as medieval ladies, pirates, and, of course, angels.
Another type of "sleeve" is when a tattoo design covers the arm from the shoulder to the elbow or from the shoulder to the wrist. These "sleeves" are often referred to by their subject matter, which could be anything from monsters to pinups to angels. Thus, an angel sleeve can also refer to a tattoo covering most of the arm whose subject is an angel.