This Editorial Commentary written for Pediatric Critical Care Medicine (1) is “Part 5” of five focused comments (2–5) about the original Phoenix Sepsis Criteria work published in the Journal of the American Medical Association in February 2024 (6). “Part 1” contained an overview of the evolution in definition of sepsis and septic shock from representative of the Society of Critical Care Medicine (SCCM) Pediatric Sepsis Definitions Taskforce (2). “Part 2” commented on using “interventions” in the criteria (3); “Part 3” is a discussion on using “stages of sepsis” in the criteria (4); and “Part 4” covered using “world orientated” criteria for sepsis (5).

Now, in “Part 5,” we comment and discuss using “parsimony” in the definition of sepsis. For example, one main aim when developing the Phoenix criteria was to consider the needs of clinicians around the world caring for children. We needed to redefine the complex, heterogeneous disease that is called “sepsis,” with the goal of it being globally relevant and parsimonious but not too simplistic (see “Part 3” in this series of commentaries [4]). Throughout the process, there was tension in reaching consensus due to trade-offs arising between parsimony—choosing the simplest explanation for the syndrome called sepsis—vs. facing the challenge of explaining its inherent complexities. Therefore, in “Part 5”—the last in this series—we highlight four questions and the debate that arises when redefining sepsis in children.