MACD stands for moving average convergence divergence. This is a technical indicator that was created in the 1970s by Gerald Appel, originally designed for stock chart analysis.
The MACD is an unbound oscillator that displays 2 lines moving over a zero level plane. The faster Line is the MACD Line, and the slower line is the Signal line.
The MACD Line demonstrates momentum and direction by comparing current price with historical price. When current price is unchanged from historical price, there is no momentum and no direction. But, when the market takes off in one direction, there is a growing difference between current price and historical price, which is illustrated with the MACD Line climbing away from zero.
The Signal Line is keeping track of the MACD Line. When there has been no change in momentum or direction for a length of time, the Signal Line catches up to the MACD Line, demonstrating lack of decision for direction and lack of momentum.