what does the half blood prince mean in harry potter
Before leaving Hogwarts to accompany Dumbledore in locating another horcrux -- part of Voldemort's soul -- Harry discovers from Professor Trelawney that it was Snape who overheard the prophecy and told it to Voldemort, resulting in Voldemort hunting down Harry and his parents. Despite this and Harry's angry questions, Dumbledore avers his trust in Snape. Returning to Hogwarts after retrieving Voldemort's Horcrux, Harry and Dumbledore alight atop the school's astronomy tower. Gravely weakened by the horcrux's protective potion, Dumbledore tells Harry he must fetch Snape, but before Harry can leave, Draco suddenly arrives, intending to carry out Voldemort's order to assassinate Dumbledore, closely followed by other Death Eaters (followers of Voldemort), and Snape. Snape interrupts the planned murder, killing the headmaster himself. Harry, who is paralysed under his invisibility cloak by Dumbledore for his own protection, witnesses the kill, and is released upon Dumbledore's death. Enraged, he pursues Snape, Draco, and the Death Eaters as they flee the castle. Snape easily blocks Harry's spells and jeeringly points out Harry's mistakes, but never strikes back. During the confrontation, Snape reveals himself as the eponymous "Half-Blood Prince" (being the half-blood son of Muggle Tobias Snape and pure-blood Eileen Prince). Snape passes through the school gates and Disapparates with Draco in tow at the book's end. The full relationship between Dumbledore and Snape and the reason for Snape's actions remain unknown until the final book. In an interview, Rowling mentioned that at this point in the series, the Harry -- Snape relationship has become "as personal, if not more so, than Harry -- Voldemort."