To write as clearly as possible, it is important to have a common language for definitions and terminology. The Lean system (which includes Hoshin kanri (A more precise definition is found in the Glossary (See No. 3))) and parts of digital systems (with a specific focus on Artificial Intelligence, Industries 4.0 and 5.0) are described here, holistically and then in detail for their various key components. In addition, a glossary is included at the end of chapters, giving a quick summary. This chapter is about clarifying the “what” question and analyzing criteria concerning performance. The meaning, the raison d'être of its approaches, and their implementation for their part are addressed from Chap. 5 onwards.