A "flashing light", by the definition given in the rules, is a light that __________.

A "flashing light," according to the navigation rules, is defined as a light that flashes at regular intervals at a frequency of 120 flashes or more per minute. This definition is important for distinguishing between different types of navigational lights on vessels, as the frequency and cadence of the flashes provide critical information about the light's purpose, location, and the nature of the hazards it may signify.

The significance of this definition lies in its application to safe navigation. For example, a flashing light at this frequency is often used to alert mariners to navigational hazards or indicate specific locations, such as safe passages or potential dangers in the water. The consistency and regularity of the flashing also help mariners to recognize the light quickly and respond appropriately, which is crucial in maintaining safety at sea.

Other options outline varying definitions of a flashing light; however, they do not meet the precise description required by the rules. Hence, option B stands out as the correct answer.