Calendar anomalies refer to the patterns or trends in financial markets that occur at specific times of the year or month. These anomalies are not explained by fundamental factors or market efficiency and are often attributed to behavioral biases or institutional factors. Some examples of calendar anomalies include the January effect, where stock prices tend to rise in January, the weekend effect, where stock returns are lower on Mondays, and the holiday effect, where stock returns are higher during the holiday season. These anomalies have been studied extensively by researchers and have implications for investment strategies and market efficiency.