In physics, the reciprocal lattice of a lattice (usually a
Bravais lattice) is the lattice in which the Fourier Transform of
the spatial function of the original lattice (or direct lattice) is
represented. This space is also known as momentum space or less
commonly k-space, due to the relationship between the Pontryagin
momentum and position. The reciprocal lattice of a reciprocal
lattice is the original or direct lattice.