This document discusses different types of definitions and how to write them effectively. It begins by explaining that precise definitions of key terms are important for clear communication. It then describes essential definitions, which name the item, place it in a broad category, and distinguish it from others in that category. The document notes some pitfalls to avoid in essential definitions and explains that extended definitions using various writing techniques are sometimes needed to fully explain abstract concepts. It concludes by mentioning that negation can also be used in extended definitions.