hard rock vs music

hard rock

noun
  • A rock music genre marked by a heavy regular beat, high amplification, and usually frenzied performances. 

music

noun
  • A series of sounds organized in time, usually employing some combination of melody, harmony, tempo, rhythm etc. usually to convey a mood. 

  • An art form, created by organizing of pitch, rhythm, and sounds made using musical instruments and sometimes singing. 

  • Any pleasing or interesting sounds. 

  • Electronic signal jamming. 

  • A guide to playing or singing a particular tune; sheet music. 

verb
  • To seduce or entice with music. 

How often have the words hard rock and music occurred in a corpus of books? (source: Google Ngram Viewer )