rsi, stochastic-oscillator, williams-percent-r and commodity-channel-index are all oscillators. They normalise recent price movement onto a fixed scale so that extremes can be compared across time and instruments.
Oscillators work best in trading-range conditions, where fading extremes has some basis, and worst in trends, where they pin at one end and stay there. The most common beginner mistake in all of technical analysis is shorting a strong uptrend because an oscillator reads overbought.
They are also derivatives of price, so they add no information; they reframe it. Two oscillators on the same chart usually agree, which creates a false impression of confirmation. See chart-clutter.
Related: overbought, oversold, momentum-indicator, chart-clutter, trading-range