From Online Dictionary of Crystallography
Distance interplanaire (Fr). Netzebenenabstand (Ge). Distanza interplanare (It). 面間距離 (Ja). Distancia interplanar (Sp).
The interplanar spacing or interplanar distance is the perpendicular distance between two successive planes on a family (hkl). It is commonly indicated as dhkl and corresponds to the reciprocal of the length of the corresponding vector in reciprocal space:
where G* is the metric tensor in reciprocal space and T stands for transposed vector.