why is electromagnetic spectrum called continous?

Question: why is electromagnetic spectrum called continous?
- Keywords:
  electromagnetic,
  spectrum
Asked by 698bm1924 to Peter, Jonathan, Grace, Doris, David, Ann on 6 Jun 2019.
- Grace Kago answered on 6 Jun 2019:
  
  continuous here is to refer to an interval of real numbers, aka the wavelengths in the electromagnetic spectrum differ by a fixed number with no gaps!
  
  Source: https://study.com/academy/lesson/continuous-spectrum-definition-lesson-quiz.html

Question: why is electromagnetic spectrum called continous?