Phase transitions occur both in the course of the system life cycle (Fig. 3.1) and in the problem-solving cycle (Fig. 3.23) and are referred to differently depending on the context: In Project Management (DIN 69901-2:2009-01, p. 11), for example, they are referred to as milestones, in Systems Engineering also as decision thresholds (Walden et al. 2023, pp. 29 ff.), Robert G. Cooper (2002, pp. 128 f.) calls them gates and Nadin Ebel (2011) control points. Clear definitions and clear demarcations from one another or references to one another are only partially found. In essence, however, all designations mean the same thing.