What is the background of the terminology of [spectra][1] in homotopy theory? In what extend does the name "spectrum" fit to the definition and the properties? Also, are there relations to other spectra in mathematics (algebraic geometry, operator  theory)?

PS: The title is an allusion to [this question][2] ;-)
 
  [1]: http://en.wikipedia.org/wiki/Spectrum_(homotopy_theory)
  [2]: http://mathoverflow.net/questions/17357/what-is-so-spectral-about-spectral-sequences