Abbreviation for Relative Strength Index. A technical analysis tool that compares the magnitude of price rises of a security with the magnitude of price falls so as to identify overbought and oversold signals. It acts as a warning when there is a divergence between movements in the Relative Strength Index and movements in the security's price. For example, the RSI may be rising when the price of the security is falling, giving a buy signal.

See also: Momentum Oscillator