Zettelkasten
Definition
Any Zettelkasten is based on the work of Niklas Luhmann, a sociologist. He was a prolific writer, and attributed much of his abundant creativity to his use of a slip box (see Niklas Luhmann’s Card Index: Thinking Tool, Communication Partner, Publication Machine.
His slip box (a filing cabinet of cards – hence zettle (note) kasten (cupboard)), was unique because instead of filing the cards in a typical hierarchical way, he gave each card a unique identifier (usually a date number) and then cross-referenced this note to other related ideas as they emerged.