What does Sr mean on a Nissan Sentra?

There are four trim levels: S, SV, SR and SL. The base model S has air-conditioning, full-power accessories and an auxiliary audio jack. The SV doesn't add much in the way of standard equipment, but rather increases the availability of options. The SR is essentially an SV with sporty design elements, while the SL gets the sort of luxury and convenience items that have begun showing up in this segment.