“A ventilated double facade can be defined as a traditional single facade doubled inside or outside by a second, essentially glazed facade. Each of these two facades is commonly called a skin (Whence the widely-used name “ventilated double-skin facade”). A ventilated cavity - having a width which can range from several centimetres at the narrowest to several metres for the widest accessible cavities - is located between these two skins.
There exist facade concepts where the ventilation of the cavity is controllable, by fans and/or openings, and other facade concepts where this ventilation is not controllable (the ventilation is produced in this case via fixed permanent ventilation openings). The indoor and outdoor skins are not necessarily airtight (see, for example, the “louver” type facades). Automated equipment, such as shading devices, motorised openings or fans, are most often integrated into the facade. The main difference between a ventilated double facade and an airtight multiple glazing, whether or not integrating a shading device in the cavity separating the glazings, lies in the intentional and possibly controlled ventilation of the cavity of the double facade”.
[Belgian Building Research Institute [BBRI]: Ventilated double facades – Classification and illustration of facade concepts, Department of Building Physics, Indoor Climate and Building Services, (2004)]

“Essentially a pair of glass “skins” separated by an air corridor. The main layer of glass is usually insulating. The air space between the layers of glass acts as insulation against temperature extremes, winds, and sound. Sun-shading devices are often located between the two skins. All elements can be arranged differently into numbers of permutations and combinations of both solid and diaphanous membranes”.
[Harrison K. & Meyer-Boake T.: The Tectonics of the Environmental Skin, University of Waterloo, School of Architecture, (2003)]

“The Double Skin Façade is a system consisting of two glass skins placed in such a way that air flows in the intermediate cavity. The ventilation of the cavity can be natural, fan supported or mechanical. Apart from the type of the ventilation inside the cavity, the origin and destination of the air can differ depending mostly on climatic conditions, the use, the location, the occupational hours of the building and the HVAC strategy. The glass skins can be single or double glazing units with a distance from 20cm up to 2 meters. Often, for protection and heat extraction reasons during the cooling period, solar shading devices are placed inside the cavity.”
[Harris Poirazis: Double Skin Façades for Office Buildings – Literature Review. Division of Energy and Building Design, Department of Construction and Architecture, Lund Institute of Technology, Lund University, Report EBD-R--04/3, (2004)]