Invisibility

Invisibility is the state of a physical object being magically unseen. Wizards reach it by several routes: an Invisibility Cloak, the Invisibility Spell, or a Disillusionment Charm or Bedazzling Hex, both of which come close enough to pass. The Hogwarts library keeps an entire Invisibility Section, where the books discuss the subject and are themselves invisible, an arrangement that has caused real difficulty for booksellers trying to count their stock. Some invisibility is conditional rather than absolute, working on certain onlookers and not others. Thestrals stay unseen by anyone who has not witnessed death, and Dementors are invisible to Muggles and Squibs while witches and wizards see them plainly.