In architecture, a boss is a knob or protrusion of stone or wood.
One common example of a boss can be found in the ceilings of buildings, particularly at the intersection of a vault. In Gothic architecture, such roof bosses (or ceiling bosses) were often intricately carved with foliage, heraldic devices or other decorations. Many feature animals, birds, or human figures or faces, sometimes realistic, but often grotesque: the Green Man is a frequent subject.
Bosses were also an important feature of ancient and Classical construction.
When stone components were rough-cut onsite at quarries, they were usually left with bosses (small knobs) protuding on at least one side. This allowed for easy transport of the materials to the site; once there, the bosses also facilitated raising and/or inserting the pieces into places.
An excellent and still extant example of such bosses can be seen at the Greek Doric temple of Segesta, at which construction was never completed. The bosses of several key elements of the temple, notably the crepidoma, remain as a testament to the construction process.