The relative strength index (RSI) is a momentum indicator, scored from 0 to 100, that measures the speed and size of a stock’s recent price changes to gauge whether it has been rising or falling unusually fast relative to its own recent history.
Readings above 70 are conventionally described as overbought, and readings below 30 as oversold — both are read as signs that a price move may be due for a pause or reversal, though neither is a guarantee, especially during a strong trend.
RSI is one of the more common tools in technical screening, usually paired with moving averages rather than used alone. See technical indicators as screening criteria for how it fits into a broader technical screen.