Background: Pre-loading of alcohol and other drugs has become a prevalent start to nights out in many countries. Studies into pre-loading have been using different operational definitions and descriptions, leading to confusion and debate in the research literature. Purpose/Objective: We wish to propose a full taxonomy so that research into preloading, of any substances, can be specific and standardized. Methods: We address this problem by analyzing (1) terminology used throughout the literature, (2) the evolving nature of this phenomenon, and (3) the operational components comprising this substance use practice. Additionally, we provide a context and rationale for how we view pre-loading in relation to the broader event-level session. Results: Our results propose a full operational definition and taxonomy of pre-loading to be used, and built upon, by researchers. We also provide a visual representation of pre-loading within an event-level session and provide a method to facilitate consistency across cultures. Conclusions: We propose that this system will lead to greater specificity and higher reliability in the interpretation of research results.