Question: What was a previous unoffical name for the high performance variant of Audi's compact executive car?

Context paragraphs:
Sports sedan: A sports sedan or a sports saloon is a sedan automobile (US) or saloon car (UK) that is designed to look and feel "sporty", offering the motorist more connection with the driving experience, while providing the comfort and amenities expected of a luxury sedan.  A wider definition that includes related coupé, convertibles, crossovers is known as sport luxury.  Most vehicles in this category overlap with the compact executive car and executive car classifications, while the sporty small family sedans are called sport compacts (mostly used in North America).

Mercedes-Benz C-Class (W202): Mercedes-Benz W202 is a compact executive car which was produced by the German automaker Mercedes-Benz in 1993–2000, under the C-Class model names.  In May 1993, the first generation Mercedes-Benz C-Class was introduced as a replacement for the 190.  The C-Class sedan was the company's entry-level model up until 1997, when Mercedes-Benz launched the smaller A-Class.  Styling themes were carried over from the previous W201 series, but the new series had a smoother and rounder design than the previous generation of the compact Mercedes-Benz.

Audi RS 4: The Audi RS4 quattro is the top tier and highest performing version of some specific generations of the Audi A4 range of automobiles.  It is a sports-focused compact executive car (often called sport compact in some countries ), produced by Audi's high-performance private subsidiary quattro GmbH, in limited numbers, for German car manufacturer AUDI AG, part of the larger Volkswagen Group.  It slots distinctly above the Audi S4, as the fastest, most sports-focused model based on the A4's "B" automobile platform.  The RS 4 made a comeback in 2012, in Avant form only based on the Audi A4 Avant.

Audi S4: The Audi S4 is the high performance variant of Audi's compact executive car A4.  The original Audi S4, built from 1991 until 1994, was a performance-oriented version of Audi's 100 saloon/sedan.  All subsequent S4s since 1997 have been based on the Audi A4; and as the A4 has evolved from one generation to the next, so has the S4.

Audi 80: The Audi 80 is a compact executive car produced by the German manufacturer Audi (initially known as Auto Union and Audi NSU Auto Union) from 1966 to 1996.  It shared its platform with the Volkswagen Passat from 1973 to 1986 and was available as a sedan, and an Avant (Audi's name for a station wagon).  The coupé and convertible models were not badged as members of the range but shared the same platform and many parts.

Audi Ur-S4 / Ur-S6: Audi Ur-S4, and Audi Ur-S6 were unofficial names for the original models of the Audi S4 and S6 automobiles.

Audi A6: The Audi A6 is an executive car made by the German automaker Audi AG, now in its fourth generation.  As the successor to the Audi 100, the A6 is manufactured in Neckarsulm, Germany – and is available in sedan and wagon configurations, the latter marketed by Audi as the "Avant."  Audi's internal numbering treats the A6 as a continuation of the Audi 100 lineage, with the initial A6 designated as a member of the C4-series, followed by the C5, C6, and the C7.  The related Audi A7 is essentially a coupé-hatchback version of the C7-series A6, but is marketed under its own separate identity and model designation.

Compact executive car: A compact executive car is a premium car smaller than an executive car.  In European classification, compact executive cars are part of the D-segment.  In North American terms, close equivalents are "compact premium car", "compact luxury car", "entry-level luxury car" and "near-luxury car".  Compact executive cars are usually available in saloon, estate, coupé, and cabriolet body styles.

Audi S6: The Audi S6 is the high performance variant of the Audi A6, an executive car produced by German automaker Audi.  It went on sale in 1994, shortly after the "A6" designation was introduced, replacing the "100" nameplate.

Alfa Romeo Giulia: Alfa Romeo Giulia (] ) is the name of three not directly related models by the Italian car manufacturer Alfa Romeo.  The first is a line of sporty four-door compact executive cars (Type 105) produced from 1962 to 1978, the second is an updated, mainly up-engined Spider, Sprint and Sprint Speciale Giuliettas, and the third Giulia is a compact executive car (type 952) unveiled in 2015.

Supporting paragraphs: Audi Ur-S4 / Ur-S6 Audi S4
Answer: Audi Ur-S4