Enteral feeding intolerance (EFI) is a common feature in critically ill patients worldwide. However, there is no clear, widely agreed-upon definition available, with various studies rarely using the same definition. The term EFI is frequently used to describe vomiting or large gastric residual volumes associated with enteral feeding as a result of gastroparesis/delayed gastric emptying. However, the syndrome of EFI may represent the consequence of various pathophysiological mechanisms, and this heterogeneity may explain varying associations with outcomes. In clinical practice, a pragmatic definition may be useful. A pragmatic definition of EFI is that a clinician has decided to reduce the amount of enteral nutrition specifically because features of gastrointestinal dysfunction appeared during enteral feeding. For research purposes, a more detailed definition of EFI is required to improve knowledge and explore interventions that may improve patient-centered outcomes. The objective of this review is to summarize available evidence on existing definitions, pathophysiological mechanisms, and the clinical relevance of EFI in critically ill patients. Based on current knowledge, we propose a conceptual framework for a definition of EFI for a future consensus process.