Fleeting, literature and permanent notes are the note types in Sönke Ahrens' Zettelkasten workflow, which moves an idea from quick capture, through notes on what one reads, into lasting notes kept in a slip-box.
Ahrens sets out the workflow in his book How to Take Smart Notes, covered in 📝Smart Notes (Ahrens), which aims to make the 📝Zettelkasten of 📝Niklas Luhmann accessible to anyone interested in reading, thinking and writing.
In Ahrens' words, "Fleeting notes are there for capturing ideas quickly while you are busy doing something else." They are temporary: Ahrens expects them to be discarded within a day or two, once the idea has been recast as a lasting note.
Permanent notes are the opposite. Ahrens describes them as notes "which will never be thrown away and contain the necessary information in themselves," stored "either in the reference system or, written as if for print, in the slip-box," and written in one's own words. That standard overlaps with 📝atomic notes, which are written to be understood on their own.
Literature notes sit between the two, and readers disagree on how cleanly they separate from permanent notes. F. Lengyel's 2022 guest post on zettelkasten.de reads the book's main categories as fleeting, permanent and project notes, and counts a literature note, a source reference kept in a reference manager, as a subcategory of permanent notes. In that reading a fleeting note may become a literature note and then a permanent note, or go to the slip-box directly.