D-size

D is short for what is usually called the Delaney symbol or Delaney-Dress symbol or the Delaney-Dress-Delgado symbol, that is used to encode the topology of a tiling. The size is the number of distinct (not symmetry-related) chambers in the tiling, and is the same as the flag transitivity. A regular tiling has D-size of 1 (check what tilings are regular). See also the meaning of regular net in the pop-up for keywords.