The month during which there is the greatest trading activity in derivatives trading. These derivatives can be options, futures, or other type of derivative-based instruments. The occurrence of a blue month is typically of interest to hedge funds and large financial institutions because the volume of derivative trading can be used as a technical trading signal.

Volumes of daily traded shares are much more accessible than the volume of daily derivative trading. However, options and futures trading activity is also publicly accessible to keen investors. The month when the volume of derivative trading is highest is referred to as the blue month.