In statistics, many time series exhibit cyclic variation known as seasonality, seasonal variation, periodic variation, or periodic fluctuations. This variation can be either regular or semi-regular.

Seasonality, Fasting Endurance, and Body Size in Mammals
SEASONALITY EXTRACTION FROM TIME-SERIES OF SATELLITE SENSOR DATA
Capital market seasonality: The case of stock returns
Insect seasonality: circle map analysis of temperature-driven life cycles.
Seasonality extraction by function fitting to time-series of satellite sensor data
Size-related anomalies and stock return seasonality : Further empirical evidence
Further Evidence On Investor Overreaction and Stock Market Seasonality
Further Evidence On Investor Overreaction and Stock Market Seasonality
Further Evidence on Investor Overreaction and Stock Market Seasonality. "Journal of Finance, 42
Adaptation to Seasonality in a Cricket: Patterns of Phenotypic and Genotypic Variation in Body Size and Diapause Expression Along a ...