The definition of quasicrystals
  It is argued that the definition of quasicrystals should not include the requirement that they possess an axis of symmetry that is forbidden in periodic crystals. The term "quasicrystal" should simply be regarded as an abbreviation for "quasiperiodic crystal," possibly with two provisos, as discussed below. The argument is supported by theoretical as well as experimental examples of quasicrystals without any forbidden symmetry. 
Ron Lifshitz (Tel Aviv University)