A weather condition known especially in the US South when the temperature is over 100 degrees, or the heat index is over 100 degrees, or the humidity plus the temperature make it feel like it is over 100 degrees and you are in the jungle. This condition also causes "monkey-butt."
I went to Jazz Fest in New Orleans the first weekend in May and it was ball searing hot! I nearly passed out from the heat! Luckily there was plenty of cold beer.