background vs front line

background

adj
  • Less important or less noticeable in a scene or system. 

noun
  • One's social heritage, or previous life; what one did in the past. 

  • Information relevant to the current situation about past events; history. 

  • The image or color over which a computer's desktop items are shown (e.g. icons or application windows). 

  • A part of the picture that depicts scenery to the rear or behind the main subject; context. 

  • A less important feature of scenery (as opposed to foreground). 

  • A type of activity on a computer that is not normally visible to the user. 

verb
  • To put in a position that is not prominent. 

  • To gather and provide background information (on). 

front line

noun
  • A low level. 

  • attack, collectively the attackers or forwards. 

  • A site of a conflict, effort, or controversial matter of any kind. 

  • A front, or a boundary between opposing positions. 

  • The site of interaction with outsiders, such as customers. 

How often have the words background and front line occurred in a corpus of books? (source: Google Ngram Viewer )