The Green Mile

In a Louisiana assisted-living home in 1999, Paul Edgecomb begins to cry while watching the film Top Hat. His companion Elaine becomes concerned and Paul explains to her that the film reminded him of the events of 1935, which took place when he was a prison officer, in charge of death row and the state's electric chair.
In 1935, Paul supervises fellow officers Brutus "Brutal" Howell, Dean Stanton, Harry Terwilliger and Percy Wetmore at Cold Mountain Penitentiary on what they refer to as the "Green Mile", Death Row. Paul is suffering from a severe bladder infection and receives John Coffey, a physically imposing but mentally challenged black man, into his custody. John had been convicted of raping and murdering two little white girls. One of the other inmates is a Native-American named Arlen Bitterbuck, who is charged with murder and is the first to be executed. Percy demonstrates a severe sadistic and bullying streak but is beyond reproach; he is the nephew of Louisiana's First Lady, but only Paul is bold enough to defy this. He is particularly abusive with inmate Eduard "Del" Delacroix; he breaks Del's fingers with his baton, steps on a pet mouse named Mr. Jingles, which Del had adopted, repeatedly calls him by a gay slur, and ultimately sabotages his execution by failing to soak the sponge used to conduct electricity to Del's head; Del's body explodes in flames and he dies screaming in pain.
John begins to demonstrate supernatural powers; he cures Paul's bladder infection, resurrects Mr. Jingles, and heals Melinda Moores, wife of the prison's chief warden, of a brain tumor. This last affliction he releases into Percy, who under its influence shoots another prisoner, mass murderer William Wharton, dead. Wharton had from the moment of his arrival been a troublemaker; he attacked the guards as he was being escorted into the block, made mischief on two occasions later which caused Paul to order him restrained in the block's padded cell, groped Percy briefly, racially insulted John, and revealed psychically to John that he is in fact responsible for the crime for which John was unjustly condemned. John then reveals the story psychically to Paul, but in so doing releases his supernatural energy into Paul. Meanwhile, Percy is committed to the insane asylum which Wharton had come from.
Distraught over the notion of executing an innocent man, John tells Paul that he does in fact wish to die as he views the world as a cruel place. Mentioning that he had never seen a movie before, John watches Top Hat with the other guards as a last request. John is executed that night, although he refuses the customary hood as he is afraid of the dark. Paul concludes his story by telling Elaine that John's was the last execution that either he or Brutus supervised; following Coffey's execution they both took jobs in the juvenile system.
Elaine realizes that, since he had a grown son in 1935, Paul must be much older than he looks. Paul reveals that he is in fact 108 years of age. Not only is he still alive, so is Del's mouse, Mister Jingles. Paul then muses that if John's power could make a mouse live for as long as Mr. Jingles has, how much longer does he himself have left?

Question: What does the term "Green Mile" refer to?
Answer: Death Row