There was an appearance of Human Target on Arrow to protect the mayor Oliver Queen and there also is a TV series of the same name, are they related to each other? If yes what are the references of the TV series given in the Arrow episode.
First need to note that Human Target is a DC comic book character.
The Human Target is the name of two fictional characters appearing in American comic books published by DC Comics. The first is Fred Venable, who appears in Detective Comics #201 (November 1953), by Edmond Hamilton and Sheldon Moldoff.
The second, Christopher Chance, first appears in Action Comics #419 (December 1972), and was created by Len Wein and Carmine Infantino. This character, a private investigator and bodyguard who assumes the identities of clients targeted by assassins and other dangerous criminals, has appeared in numerous books published throughout the decades, and has appeared in television adaptations.
But out of this two, only Christopher Chance got live action adaptation.
Now come to your question:
What is the relationship between Human Target TV series and the Human Target appeared in Arrow season 5?
And the answer is all three portrayal are based on same DC comic book character but share no direct relation or chronology and even portrayed by different actors.
Arrow TV show have it's own universe called Arrowverse and share close continuity with them, refer arrowverse tag wiki for more information.