<p><a href="https://stats.stackexchange.com/search?q=cycle%20time-series">Searching for cycle and time-series</a> I receive 339 results. Cycles are an important pattern in time-series analysis and therefore I think that they should receive their proper tag.</p>

<p><strong>Edit</strong>: The difference between a cycle and a seasonality is that a seasonality always appears after the same time period. One example is that Christmas always appears once a year in December. Also every Sunday Christians celebrate Sunday. However a cycle appears in irregular time periods, e.g., business cycles where recession appears more or less twice a decade are an example. </p>

<p>See also <a href="https://www.otexts.org/fpp/6/1" rel="nofollow noreferrer">here</a>:</p>

<blockquote>
  <p><strong>Seasonal</strong><br>
  A seasonal pattern exists when a series is influenced by seasonal factors (e.g., the quarter of the year, the month, or day of the week). Seasonality is always of a fixed and known period.</p>
  
  <p><strong>Cyclic</strong><br>
  A cyclic pattern exists when data exhibit rises and falls that are not of fixed period. The duration of these fluctuations is usually of at least 2 years.</p>
</blockquote>

<p>@robjhyndman what do you think as an expert in this area?</p>
