Effective perioperative hemostasis in pediatric cardiac surgery depends not only on accurate diagnostics and targeted transfusion strategies but also on a clear and consistent definition of postoperative bleeding. Despite the clinical importance of bleeding in neonates and children undergoing cardiopulmonary bypass, bleeding remains variably defined across institutions, registries, and clinical trials. This heterogeneity complicates bedside decision-making, limits benchmarking, and weakens the interpretation of interventional studies. In this review, we examine postoperative bleeding definitions as a foundational component of hemostatic management in pediatric cardiac surgery. We summarize commonly used adult bleeding definitions and highlight their variability and limited applicability to neonatal and infant physiology. We review current pediatric approaches, including chest tube output-based thresholds and multidimensional severity scales that incorporate clinical impact and physiologic consequences, while avoiding reliance on transfusion or procedural interventions alone. We discuss the limitations of intervention-driven criteria, the challenges of quantifying blood loss, and the influence of developmental hemostasis and surgical complexity. We also explore structural barriers within electronic medical records that impede standardized data capture and consider harmonization efforts in ECMO populations as a potential model. By outlining the consequences of definitional heterogeneity and proposing principles for standardization, this manuscript aims to support more consistent hemostatic care, meaningful benchmarking, and stronger multicenter research in pediatric cardiac surgery. We recommend that future multistakeholder consensus efforts develop a multidimensional, developmentally calibrated bleeding definition that integrates quantitative blood loss, physiologic impact, and clinical consequences while clearly separating bleeding severity from the interventions used to treat it.