“The Chosen One” was a title applied to Harry Potter in reference to Professor Trelawney’s prophecy about an individual destined to defeat or be defeated by Lord Voldemort. However, the wording of the Prophecy meant that the actual Chosen One could have been either Harry or his classmate Neville Longbottom (JKR-FAQ).
During the Summer holidays in 1996, the Daily Prophet ran an article entitled “HARRY POTTER: THE CHOSEN ONE?” (HBP3). This caused some unpleasant (but also some good-natured) teasing of Harry as the “Chosen One” when he was back in Hogwarts School for fifth year (HBP7, HBP8, HBP9, HBP11).
Notes and interesting facts
When Harry was using Felix Felicis to get a memory from Horace Slughorn, the latter drunkenly referred to Harry as "Parry Otter, the Chosen Boy" (HBP22).
As the Minister for Magic, Rufus Scrimgeour tried to convince Harry to use his fame as the "Chosen One" to raise the popularity level of his administration (HBP16).
Daily Prophet reporter Rita Skeeter was still referring to the grown-up Harry as the "Chosen One" in her article "Dumbledore’s Army Reunites At Quidditch World Cup Final" before the last match of the 2014 tournament (QWC).