heat wave

Short definition from Wiktionary

Noun

1. 1
   A period of exceptionally hot weather.
2. 2
   A period of exceptionally hot weather: Three consecutive days with daytime high temperature of 90 degrees Fahrenheit or higher.
3. 3
   A period of exceptionally hot weather: A period of at least three consecutive days with daily high temperatures of the respective county's temperature threshold or higher.
4. 4
   An electromagnetic wave in the infrared spectrum.