The MACD indicator (or "oscillator") is a collection of three time series calculated from historical price data, most often the closing price. These three series are: the MACD series proper, the "signal" or "average" series, and the "divergence" series which is the difference between the two.
The MACD series is the difference between a "fast" (short period) exponential moving average (EMA), and a "slow" (longer period) EMA of the price series. This indicator was invented in 1979 by Gerald Appel as a tool for setting the time for stock market. Using this indicator as a predicting tool is not so popular.