What is Automotive Trim Nomenclature?

Legal Definition
Automotive trim nomenclature is loosely identified with alphanumeric lettering on various exterior locations on automobiles manufactured internationally. Some of the commonly used designations are DX, LX, LS, EX, GL, SE, GT just to name a few. The exterior coding helps identify at what level the identified vehicle is equipped. Some of the more basic lettering used is DX, while luxuriously equipped vehicles can be seen with LS, GT, or SE.

The alphanumeric coding began to appear on Japanese and European vehicles beginning in the mid 1970s, while North American vehicles used names for vehicles, such as Mustang, Torino, Impala, Chevelle, Barracuda, and Imperial. North American vehicles that were specially equipped did use special alphanumeric coding for exclusive vehicles like the "SS" designation on Chevrolet products, and Ford used the "GT" term on the high performance version of their products. GM did begin using alphanumeric coding to denote special handling packages installed on performance vehicles, such as "Z28" on the Camaro, the Buick GS, or the Oldsmobile 442, and currently uses the designation "Z71" on the Suburban and Tahoe. Toyota also uses this naming convention on the SR5.

During the 1970s and 1980s, some manufacturers used a word to denote a luxury level of equipment installed in large sedans, such as the word "Brougham" used by Cadillac Brougham, the Holden Brougham, and on the top level Nissan Cedric/Nissan Gloria.

A variation was used on numerous vehicles where the alphanumeric combination described the vehicle, such as the Mercedes-Benz 500SL. The letters "SL" represented "S-class", which is the anglicized version of "S-Klasse," a German abbreviation of "Sonderklasse," which means "special class" (in the sense of "a class of its own"). The "L" represented extended length. Later, Mercedes-Benz added an "E" to the designation "SEL" to signify that the car was installed with fuel injection, with the "E" standing for the German word "Einspritzung". The number 500 represented the engines displacement of five liters.

Another variation was used to identify various types of engine performance or technological advancements added to specially equipped vehicles. In the mid-1970s, Japanese automotive manufacturers introduced emission control technology, and used letter combinations to visually identify vehicles equipped. Some examples are Honda's CVCC, Toyota's TTC, Nissan's NAPS, and Mitsubishi's MCA. More recently, manufacturers have started using the term "hybrid" on vehicles installed with the powertrain combination.

During the mid-1980s a widely used designation was "EFI" for "electronic fuel injection" which appeared internationally, with a select few manufacturers using the lowercase letter "i" for "injection". More recently the designation "TDI" for "Turbo Diesel Injection", or "GDI" for "Gasoline Direct Injection" have appeared.

Safety equipment is also identified with letter combinations, such as "ABS" for "anti-locking brakes", or "ESC" for "electronic stability control".
-- Wikipedia