A circular piece of stained glass, often painted with a portrait or scene, is called a roundel.
Roundels are usually small, self-contained compositions set into a larger window, door or architectural opening. They may show religious subjects, saints, donors, coats of arms, trades or secular scenes. Many were made during the Renaissance and later incorporated into domestic interiors, churches and museum collections.
A roundel can be made from one main circular piece of glass or assembled from several pieces joined with lead. Painted details, including faces, folds and architectural lines, were commonly fired onto the glass so that they became permanent.
The term is easy to confuse with quarry, which refers to a small square or diamond-shaped pane, and lancet, which describes a tall, narrow window opening. Roundel identifies the circular format rather than a particular colour or manufacturing process.