backlog vs pileup

backlog

verb
  • To acquire something as a backlog, or to become a backlog 

noun
  • A reserve source or supply. 

  • A log containing text previously read, as in text-based video games or chat rooms. 

  • A large log to burn at the back of a fire. 

  • An accumulation or buildup, especially of unfilled orders, unconsumed products or unfinished work. 

pileup

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