La Canícula

Canícula. The hottest days.
That´s what it means in English according to Larousse Dictionary. That, is in a nutshell and does not demonstrate the length and the extreme of this term.
According to http://www.todito.com/paginas/noticias/88369.html
(in free translation): During the canícula, the heat is unbearable, the people sweat constantly, the animals go about with their tongues hanging out of their mouths, and others become crazy.
These high temp. can go beyond the 40´s (Celsius), starting mid June till the end of August.

Basically you want to die.

Here is another interesting definition from wikipedia:

clipped from en.wikipedia.org

The name of this star comes from the Latin Sīrius, from Greek Σείριος (Seirios, "glowing" or "scorcher").^[18] As the major star of the "Big Dog" constellation, it is often called the "Dog Star".

The Latin name for this star is Canicula ("little dog")

Historically, many cultures have attached special significance to Sirius. Sirius was worshipped as Sothis in the valley of the Nile long before Rome was founded. The Middle Kingdom of Egyptians based their calendar on the heliacal rising of Sirius, which occurred just before the annual flooding of the Nile and the summer solstice.^[19] In Greek mythology, Orion's dog became Sirius. The Greeks also associated Sirius with the heat of summer: they called it Σείριος Seirios, often translated "the scorcher." The dog days of summer were also connected to Sirius.