A diurnal cycle in which an individual is awake and active for approximately 30 hours (or at any rate, more than 24, on a consistent basis) and asleep for 15 (or at any rate, more than 12, on a consistent basis). This cycle, while sustainable for considerable periods of time (dependent on caffeine, will, and usually access to Turner Network Television (TNT)), tends to lead towards psychosis, or at any rate abnormal behavior and surprising variations in perception, thought, etc.
Nick has done extensive experimentation with the 15/30 day, at considerable personal cost, resulting in a lot of amusement.