From Online Dictionary of Crystallography
Groupe sous-périodique (Fr); Gruppo subperiodico (It).
A subperiodic group is a group of Euclidean mappings such that its translations form a lattice in a proper subspace of the space on which it acts.
A crystallographic subperiodic group in n-dimensional space is a subperiodic group for which the group of linear parts is a crystallographic point group of n-dimensional space. The crystallographic subperiodic groups in two and three-dimensional space are classified in:
- frieze groups: 7 two-dimensional groups with one-dimensional translations;
- rod groups: 75 three-dimensional groups with one-dimensional translations;
- layer groups: 80 three-dimensional groups with two-dimensional translations.
International Tables of Crystallography, Volume E