recurring sequence of events or states that returns to its starting point
biogeochemical cycles: carbon cycle, nitrogen cycle, water cycle, phosphorus cycle
metabolic cycles: Krebs cycle (citric acid cycle), Calvin cycle, urea cycle
astronomical cycles: day/night, lunar month, solar year, Milankovitch cycles
economic cycles: expansion, peak, contraction, trough (Kondratiev, Juglar, Kitchin waves)
life cycle: birth, growth, reproduction, death -- applies to organisms, products, technologies
block production cycles in distributed ledgers: propose, validate, finalize, repeat
hysteresis: some cycles do not return to the exact starting state, path-dependence matters
oscillation is a continuous cycle; discrete cycles proceed in distinct steps