|"Is this all real? Or has this been happening inside my head?"
The subject of this article is a real-life person, 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.
Bonniers Konversationslexikon was a Swedish encyclopedia published in the 1920s, in twelve volumes. Headmaster Albus Dumbledore kept a copy of this encyclopedia in his office at Hogwarts Castle, in the 1990s. Remus Lupin also kept a copy in his office.