- 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