Sentence:  "We're havin a <WSD>heat wave</WSD> / A tropical <WSD>heat wave</WSD> / The temperatures rising, it isn't surprising / She certainly can, can can! / She started a <WSD>heat wave</WSD> / By letting her seat wave, / in such a way that the customers say / that she certainly can, can-can!" 
Meaning of the word marked with <WSD> tags:  A period of exceptionally hot weather.