It is not unreasonable to think of a platform as a latter-day chassis - a basic structural and mechanical 'architecture' subsequently clad in the visible sheet metal (etc) of the bodywork.  It's the invisibility of the elements of the platform - typically powertrains, suspensions and structural pressings such as floorpans and firewalls - which enable the widespread practise of platform sharing and the massive economies of scale to be achieved.

A commonality of around 60 percent is typical with platforms shared across brands (eg PSA Group), but as much as 90 precent can be achieved in examples of 'in-house' badge engineering.

Champions of platform sharing are the VW Group who have managed to spread their A4 platform across four brands, eight products and six different body configurations.

Where brand image is key and needs to be protected, module sharing of components within a platform (such as air conditioning systems, electrical components, safety items, etc) is an area where investment, development time and unit costs can be saved. 

This is the angle the windshield of a car slopes back from the vertical, measured at its centerline. A 'faster', more acute angle traditionally signifies a sportier kind of car.

The limit, however, is physical rather than legislative: as the screen angle increases, so too does the likelihood of internal refractions, 67 degrees being the angle at which laminated glass effectively starts to become opaque. The Lamborghini Countach was pretty much on the limit for screen angle.

The glass areas are part of a car's sculptural form, and while a screen will be substantially flat in front of the driver's eyes, double curvature may be introduced at the sides where the screen wraps round to meet the tumblehome of the side glass.

The shoulderline basically runs the length of a car's upper body side where it folds over to meet the side windows and its nature will reflect the essential character of the car. 

The surface between the shoulderline and the beltline directly below the side windows is referred to, reasonably, as the shoulder: amusingly, it is therefore below the beltline. It shouldn't be confused with the similarily-positioned haunch.

Volvo's trademark shoulders have been developed into a marque identity characteristic, which emphasizes strength - and therefore safety - a long-held Volvo byword.

See also Beltline

A shut line - or 'cut line' - is the necessary clearance gap between two adjacent exterior body panels or interior trim panels, either of which may be openable.  They may be identified individually as 'door shuts' or 'hood shuts' etc and their tightness and consistency are reliable indicators of build quality.  Continuity of surface and feature lines, and alignment of adjacent panels is now taken for granted.

Designers seize every opportunity to incorporate shut lines which will help describe a car's form and reflect its character, and which will be consistent with its surface language.

VW has the most harmonious shutlines (illus. Golf IV five-door), and BMW the most 'meandering'.

'Stance' suggests both attitude, intent and ability, confers presence, and is equally identifiable whether a car is stationary or on the move. (The apparently-similar term 'poise' refers to a car's dynamic behavior). Stance is largely defined by the body-to-wheel and the overall vehicle-to-ground relationships which are important in all cars, but vital on those for which 'attitude' is critical.

Wheels that fill a car's wheelarches in depth as well as diameter will suggest a confident stability. Wheels and wheelarches pulled out from the body sides will imply performance and even aggression, as will minimal ground clearance. Conversely, generous ground clearance is both a physical and visual requirement of an 'off-roader' vehicle.

The basic form language of the car that defines the design.

Extremes of surface language would include terms such as soft, organic and flowing or else hard-edged, geometric and boxy. It also alludes to the complexity of the surfaces eg simple, plain or busy, fussy.

Surface Language also extends to the nature of the way that the various body surfaces meet and the details within the surfaces such as grilles, lamps and other graphic elements. The language would be described by adjectives such as formal, sporty, casual, hard-edged, etc.