The term 'Holmes or Poirot' is a reference to two of the most famous fictional detectives in literature. The crossword solution for this term is 'SLEUTH, ' which is a synonym for detective. Sleuths are people who investigate and solve mysteries, often using their powers of deduction and observation. Holmes and Poirot are both examples of sleuths, and their stories have been adapted into films, television shows, and plays.