RS, relative strength, should not be confused with RSI, relative strength index.
RS is used to compare tickers to each other to determine the performance of each ticker "relative" to one another.
For example, if we're using a 90-day look-back period and QQQ is up 11% and SPY is up 7%, QQQ has a higher relative strength. Also, if QQQ was down 7% during that same period, and SPY was down 3%, SPY has higher relative strength.
At IWR, we use a variation of RS we call "VoMo", Volatility-adjusted Momentum, to assess the relative strength of tickers to each other - please see that FAQ below.
Here is a good 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. Please refer to that FAQ for more.