The MACD, or Moving Average Convergence Divergence, is a widely used technical analysis tool developed by Gerald Appel in the late 1970s. It calculates the difference between a short-term and a long-term exponential moving average, typically the 12-day and 26-day EMAs, and plots a signal line to indicate potential buy or sell opportunities. Traders use MACD to identify momentum shifts, trend direction, and possible reversals in financial markets.