oblique mark vs slash mark

oblique mark

noun
  • Synonym of slash ⟨/⟩, sometimes (generally proscribed) inclusive of similar marks such as the backslash ⟨\⟩. 

slash mark

noun
  • Synonym of slash ⟨/⟩. 

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