- A Zettel is also known as: Atomic Note, Evergreen Note, Permanent Note - A Zettel is a building block of knowledge or thought that can later be constructed to create a new piece of work. - It is discrete and self-contained. It may link to other Zettels, but on its own, it is a singular idea that can be applied to anything. - It is concept-oriented and is expressed in a complete sentence or a phrase so as to distill its meaning to the essential unit of knowledge. - A Zettel is like an API endpoint.