The D specification can appear in an ls equation specification to indicate that the equation should be estimated with fractional differencing (typically as part of an ARFIMA model).

The command:

regresses M1 on a constant, TB3, and TB3 lagged once with a first order and fourth order autoregressive component and fractional differencing.

See “Time Series Regression” for details on ARMA and seasonal ARMA modeling.

See also sar, ma, and sma.