Definition
the dog days of summer : the hottest part of summer, occurring in July and August
the dog days of summer : 夏の一番暑い時期
Example
Ex.)During the dog days of summer, it’s good to learn a new language while cooling down in doors.
夏の暑い日には、屋内で涼みながら新しい言語を学ぶのもいいよね。