Select the most appropriate meaning of the given Idiom: "Dog days of summer"

A period of dullness/inactivity

The most appropriate meaning of the idiom "Dog days of summer" is a period of dullness/inactivity. This idiom comes from the belief that the hottest days of summer were when the Dog Star, Sirius, was closest to the sun. The Dog Star was thought to bring bad luck and lethargy, and so the days when it was closest to the sun were known as the "dog days."

The other meanings of the idiom "Dog days of summer" are not as common. The meaning "fighting in summer" is not associated with the idiom "Dog days of summer" at all. The meaning "a lazy dog in summer season" is not associated with the idiom "Dog days of summer" at all.