RSI (Relative Strength Index) is a technical indicator that measures the strength and speed of a stock's price movements. It shows whether a stock is overbought (too high) or oversold (too low). The RSI scale ranges from 0 to 100, with values above 70 indicating overbought conditions and below 30 indicating oversold conditions. Traders use RSI to decide when to buy or sell a stock based on its current momentum. It's a simple tool that helps investors understand if a stock might change direction soon.