* the underside of an arch or architrave,
* the underside of a flight of stairs, under the classical entablature,
* the underside of a projecting cornice, or side of chimney
* the underside of a ceiling to fill the space above the kitchen cabinets, at the corner of the ceiling and wall,
* the exposed undersurface of any exterior overhanging section of a roof eave.
In popular use, soffit most often refers to the material forming a ceiling from the top of an exterior house wall to the outer edge of the roof, i.e., bridging the gap between a home's siding and the roofline, otherwise known as the eaves.
Soffit exposure profile on a buildings' exterior can vary from a few centimetres to well beyond a meter depending on construction. It can be non-ventilated or ventilated for cooling non livable attic space.
soffit: Published with permission from Wikipedia, the free encyclopedia