ما معنى Sandwich variance؟

The sandwich variance of an estimator defined by an estimating equation is $A^{-1}BA^{-1}$: the bread $A$, the expected derivative of the estimating equation, around the meat $B$, the variance of the equation itself. Estimated by the sample Hessian and the outer product of the per-observation scores, it is the robust (Huber–White) variance.