RS, relative strength, should not be confused with RSI, relative stregth index.
RS basically is used to compare tickers to each other to deterine the performance of each "realtive" to each other.
At IWR, we use a form of RS called VoMo, volatility adjusted momentum, to assess the relative strength of tickers to each other - please see that FAQ.
Here is a definition of RS per Investopedia:
RS, Relative strength, is a strategy used in momentum investing and in identifying value stocks. It focuses on investing in stocks or other investments that have performed well relative to the market as a whole or to a relevant benchmark. For example, a relative strength investor might select technology companies that have outperformed the Nasdaq Composite Index, or stocks that are outperforming the S&P 500 index.
We also use an indicator known as the RSI, relative strength index, to help determine overbought or oversold signals.