9.18: Twinning by psuedomerohedry
A lattice is said to be pseudosymmetric if at least a lattice row or/and a lattice plane approximately correspond to elements of symmetry; these elements can act as twinning operators (e.g., a monoclinic lattice with its oblique angle close to 90° is pseudo-orthorhombic and thus shows two pseudo twofold axes and two pseudo mirror planes).
Chapter 3.3 of International Tables of Crystallography, Volume D