The WRX TR models hit the market in 2006. TR stands for "Tuner Ready," meaning it's a stripped down version of the WRX. Although it had the same 2.5 L engine and 5 speed transmission as the WRX, it typically came with little to no options which made the price lower. It was a marketing strategy for Subaru to sell more cars cheaper and to entice the tuner crowd to purchase a "bare-bones" model since it didn't make sense to pay for all kinds of extra options when that money could be spent modifying any number of other parts on the car.
Options that the WRX typically had that the WRX TR didn't have include: performance designed front seats instead of sport designed front seats with active headrests, fog lights, rear spoiler, moon roof, leather interior, heated seats, heated side view mirrors, heated windshield wiper area, automatic climate control, premium 6 disc CD changer w/ 6 upgraded speakers instead of a single disc CD player with 4 speakers, body colored side mirrors instead of black, leather shift knob and parking handle, chrome inner door handles instead of black, rear cup holders, pocket map on passenger seat and/or center armrest extension.