Definition of "non-periodic" [non-periodic]

• Not having a regular period of repetition or orbital motion: as, non-periodic variables (stars) and comets.

The Century Dictionary (Public Domain)

• "Penrose maintains that his solution to non-periodic tiling could not have been found via an algorithmic process."
• "Shortly after that, he identified non-periodic tiling was possible with just two tile shapes."
• "They called it non-periodic tiling and the race was on to figure out who could find the least number of tile shapes that could be used for non-periodic tiling."