|"Is this all real? Or has this been happening inside my head?"
The subject of this article is a real-life person, group, company, product, or creative work that has been mentioned "in-universe" in a canon source. The Harry Potter Wiki is written from the perspective that all information presented in canon is true (e.g., Hogwarts really exists), and, as such, details contained in this article may differ from real world facts.
The Book of Psalms, also known as the Psalms of David or Psalter of David due to the majority of the psalms being historically attributed to King David, was one of the books of the Bible, featuring a collection of religious poems meant to be set to music. The Psalms of David are included as part of The Book of Common Prayer, a book found in the Hogwarts Library.