The term stained glass refers either to the material of colored glass or to the art and craft of working with it. Throughout its thousand-year history the term "stained glass" was applied almost exclusively to the windows of churches, cathedrals, and other significant buildings. Although traditionally made in flat panels and used as windows, the creations of modern stained glass artists also include three-dimensional structures and sculpture.

Modern vernacular usage has often extended the term "stained glass" to include domestic leadlight and objets d'art created from lead came and copper foil glasswork such as exemplified in the famous lamps of Louis Comfort Tiffany.

Stained glass, as an art and a craft, requires the artistic skill to conceive the design, and the engineering skills necessary to assemble the decorative piece, traditionally a window, so that it will fit snugly into the window frame for which is is made and also, especially in the larger windows, is capable of supporting its own weight and surviving the elements. Many large windows have withstood the test of time and remained substantially intact since the late Middle Ages. In Western Europe they constitute the major form of pictorial art to have survived. In this context, the purpose of a stained glass window is not to allow those within a building to see the world outside or even primarily to admit light but rather to control it. For this reason stained glass windows have been described as 'illuminated wall decorations'.