A "flashing light", according to the definition given in the rules, is a light that _____________.

A "flashing light" is defined as a light that primarily flashes at regular intervals, and thus has a specific frequency component that distinguishes it from other types of lights. According to the rules, for a light to be classified as a flashing light, it must specifically flash at regular intervals at a rate of 120 flashes or more per minute. This frequency component is essential for identifying the light's role and function in navigation, helping operators recognize it as a warning or marker.

While options referring to the color and visibility of the light may contribute to its overall characteristics and identification, they do not define the flashing mechanism itself. The color being red and visibility over a 360-degree arc are essential attributes in their context but are secondary to the defined flashing behavior. The paradigm focuses on the frequency of the flashing as the key identifier. Hence, the standout criterion for establishing a "flashing light" lies in that specific frequency, making it the correct answer for the question.