Participants in different systems frequently disagree on the precise meaning of such words as ‘planning’, ‘welfare’, ‘market’ and other socially conditioned concepts. To avoid this ambiguity, one would ideally wish to construct precise definitions of such concepts from simpler ones, starting with undefined ‘primitives’ such as ‘economic’ ‘individual,’ ‘time,’ ‘action,’ and so forth that would be unlikely to elicit disagreement among individuals participating in different systems. In this limited space, we will not be able to do this systematically. We only supply approximate definitions, which would require further refinement for any theoretical or statistical application, and suggest some examples to illustrate the significance of the concepts we introduce for comparative economic analysis. In building up definitions in this chapter, we will treat production, activity and distribution as primitives. The terms that we attempt to define more precisely are written in italics. Those that are somewhat imprecise and difficult to define are placed in quotes (e.g. ‘capitalism,’ ‘socialism’).