rs means "Rally Sport"... e.g. Camero RS also it could mean "RuneScape" as in the online game.
In Pokemon, RS, R/S or R&S stands for "Ruby And Sapphire".
As in "Pokemon Ruby / Pokemon Sapphire".
The 3 R's stand for: Reduce, Reuse, and Recycle. Perhaps the 3 Rs now stand for something else, but originally, the 3 Rs stood for (R)eading, w(R)iting, and a(R)ithmetic.
It stands for Rupees.
RS was a premium uprgrade option and special trim package that was available only on Camaros. RS stands for Rally Sport.
This will help: http://www.serebii.net/pokedex-rs/