The phrase 'Dog Days Of Summer' is used to talk about hot, sultry days.
Example of Use: “Popsicles are great for staying cool during the dog days of summer.”
The expression 'dog days of summer' is celestial in origin. The term indicates a period between July 3 and August 11 when the Dog Star, Sirius, rises at the same time or near the same time as the sun in the Northern hemisphere.