Shading coefficient (SC) is a measure of thermal performance of a glass unit (panel or window) in a building.
[1] It is an indicator of how well the glass is thermally insulating (shading) the interior when there is direct sunlight on the panel or window.
It becomes less significant in situations where direct sunlight is not a major factor (e.g., windows completely shaded by overhangs).
Window design methods have moved away from Shading Coefficient to Solar Heat Gain Coefficient (SHGC), which is defined as the fraction of incident solar radiation that actually enters a building through the entire window assembly as heat gain (not just the glass portion).
[5] A conversion from SC to SHGC is not necessarily straightforward, as they each take into account different heat transfer mechanisms and paths (window assembly vs. glass-only).