MACD is a technical indicator used in trading and investing to help identify market trends, measure trend momentum, and determine market entry points for buying or selling securities. It is based on the relationship between two exponential moving averages (EMAs) of a security's price. The MACD line is calculated by subtracting the 26-period EMA from the 12-period EMA, and a 9-period EMA of the MACD line is called the signal line. The histogram is the difference between the MACD line and its signal line. A positive value of MACD indicates that the 12-period EMA is above the 26-period EMA, and a negative value indicates that the 12-period EMA is below the 26-period EMA. The MACD is considered bullish when it crosses above its signal line and bearish when it crosses below its signal line.