A stained-glass window is any window containing colored glass. Most are divided into many very small panels, which may form pictures, designs, or abstract arrangements. Some stained-glass windows mix colored panels with clear panels. This window type is most frequently found in churches and synagogues, but is not uncommon in historic buildings in the European architectural tradition. They are sometimes referred to as leaded-glass windows because of the old practice of framing the individual bits of glass in lead.

If the glass pieces have no coloring, or are uniformly and very lightly tinted, then the window should be classified as a multi-lit window.

Colored and clear panels can occur together, and the arrangement need not form a picture. Small panels and lead framing are common, but neither is mandatory.