backslash vs separatrix

backslash

noun
  • Used erroneously in reference to, or in reading out, the ordinary slash, that is, the punctuation mark /. 

  • The punctuation mark \. 

  • |passage= […] I was trying to find a web-site for which I had been given the following address: http://www.isop.ucla.edu/pacrim/pubs/korjournal.htm. […] I began to work backwards, removing first the last part of the address following the last backslash (/korjournal.htm).}} 

verb
  • To escape (a metacharacter) by prepending a backslash that serves as an escape character, thereby forming an escape sequence. 

separatrix

noun
  • The proofreader's mark resembling a slash ⟨ / ⟩ or vertical bar ⟨ | ⟩ placed after a note in the margin to indicate that it should replace the item(s) struckthrough in the running text or to separate it from other margin notes. 

  • The ⟨L⟩ or pipe ⟨|⟩ mark formerly used to divide integers from decimals. 

  • The line between regions having different magnetic fields. 

  • The boundary separating two modes of behavior in a differential equation. 

  • A terminator: a line on a partially-illuminated surface separating the lit and shaded regions. 

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