Back in the bad old mid- to late- 1990s, "Showroom Stock" cars started to get competition adjustments in the form of "trunk kits", a kit of parts that would improve on-track performance. These initially came not as manufacturer buy sheet options but as dealer- or user-installed, and came as a box placed in the trunk upon new-car delivery (wink wink), usually consisting of easily-installed suspension parts such as springs, shocks, and swaybars.
Basically, they were under-the-table performance improvements that the manufacturer sold primary - in some cases, exclusively - to Club racers to improve their performance in Showroom Stock competition. That "wink, wink" eventually evolved into explicit dealer racer option codes (e.g., Neon ACR and Mazda "MS05" (?) codes) and soon became de facto and de jure SCCA-approved performance adjustments (even to the point where
aftermarket parts were allowed to competitors to "even the competition").
Eventually, sanity prevailed and "trunk kits" were removed. But - IMO - that led directly to the Touring class. And the originally-pejorative term "trunk kits" stuck...
GA