From Online Dictionary of Crystallography
Réseau de la macle(Fr) Reticolo del geminato (It)
A twin operation overlaps both the direct and reciprocal lattices of the individuals that form a twin; consequently, the nodes of the individual lattices are overlapped (restored) to some extent (twinning (effects of). The lattice that is formed by the (quasi)restored nodes is the twin lattice. It corresponds to the crystal lattice in twinning by merohedry and to a sublattice of the crystal (individual) in twinning by reticular merohedry.
The symmetry of the twin lattice has to be compared with the intersection symmetry of the individuals in their respective orientation, which in general is a subgroup of the group of the individual. As a consequence, the symmetry of the twin lattice may be higher, equal or lower than the symmetry of the individual lattice.
Chapter 3.3 of International Tables of Crystallography, Volume D