Definition of "heat wave"

heat wave

noun
plural heat waves
1. (idiomatic) A period of exceptionally hot weather.
  Quotations
  We're havin a heat wave / A tropical heat wave / The temperatures rising, it isn't surprising / She certainly can, can can! / She started a heat wave / By letting her seat wave, / in such a way that the customers say / that she certainly can, can-can!
  1933, Irving Berlin, “Heat Wave”, in As Thousands Cheer
2. (US, weather broadcasting) Three consecutive days with daytime high temperature of 90 degrees Fahrenheit or higher.