The Cloak of Invisibility is an invisibility cloak (canon) and one of the three Deathly Hallows (with the Elder Wand and the Resurrection Stone (canon)). The Cloak of Invisibility makes its wearer not merely invisible but truly hidden even "from the gaze of Death itself".[1] It allows in particular to hide from dementors.
The Cloak of Invisibility belonged to Ignotus Peverell and was passed down through his descendants the Potters to James Potter and then Harry Potter.[2] It does not fade with age.
Harry used it for pranks and to fight bullies, but most notably for the raid on Azkaban, where he used it to make first himself, then others, undetectable by the Dementors.
The symbol of the Deathly Hallows. The triangle represents the Cloak of Invisibility.