A planar crystallographic group or wallpaper group is a group of isometries of the plane which has a subgroup of translations that is isomorphic to ℤ2. (Compare frieze groups.)
A ‘herringbone’ wallpaper
The symmetry group of the pattern in the figure is one such wallpaper group. It contains translations and glide reflections but has no non-trivial rotational symmetry. In all there are 17 wallpaper groups (up to isomorphism).
In three dimensions there are 230 crystallographic groups and in four dimensions there are 4783.
- impartiality
- impartial spectator
- impatiens
- IMPATT diode
- impedance
- impedance coupling
- impedance matching
- impedance scaling
- impeded dune
- impedor
- impeller
- imperative
- imperative languages
- imperfect competition
- imperfect dielectric
- imperfect fungi
- imperfect((in botany))
- imperforate
- imperialism
- Imperial units
- impervious rock
- impingement separator
- implant
- implantation((in embryology))
- implementation