The latin word curiosa (plural of curiosus) means curious, inquisitive and is used to describe books or other writings dealing with strange or unusual subjects. This includes erotica (curiosa can be an euphemism for pornography) but also non-erotic writings on human sexuality, as well as other "unusual" topics. The term curiosa is a little outdated and is therefore typically used for vintage literature.
Curiosa is also a term for "interesting facts".
Books that were labeled curiosa were sometimes considered "restricted or forbidden books" that were locked away from "regular" books in libraries and archives, and were available only to selected people.
- BiblioCuriosa (a wiki on curiosa, especially French and English vintage BDSM books)