A bell sleeve can be either long or short and is usually set smoothly into the armhole (no pleating or shirring

Shirring

In sewing, shirring is two or more rows of gathers used to decorate parts of garments, usually the sleeves, bodice or yoke....

) and flares toward the bottom, where it is gathered into a band, or cuff

Cuff

A cuff is an extra layer of fabric at the lower edge of the sleeve of a garment covering the arms. In US usage the word may also refer to the end of the leg of a pair of trousers...

, by shirring or by smocking

Smocking

Smocking is an embroidery technique used to gather fabric so that it can stretch. Before elastic, smocking was commonly used in cuffs, bodices, and necklines in garments where buttons were undesirable. Smocking developed in England and has been practised since the Middle Ages and is unusual among...

. The effect is reminiscent of a bell in its shape. If the sleeve is relatively full in circumference and is gathered or pleated into both the armhole and at the bottom, it is called a Bishop's Sleeve.