Veganism is an increasingly popular lifestyle within Western societies, including Australia. However, there appears to be a positivist approach to defining veganism in the literature. This has implications for measurement and coherence of the research literature. This exploratory study assessed preference rankings for definitions of veganism used by vegan advocacy groups across an Australian convenience sample of three dietary groups (vegan = 230, omnivore = 117, vegetarian = 43). Participants were also asked to explain their ranking order in an open-ended question. Most vegans selected the UK definition as their first preference, omnivores underwent five rounds of preference reallocation before the Irish definition was selected, and vegetarians underwent four rounds before the UK definition was selected. A reflexive thematic analysis of participant explanations for their rankings identified four themes: (1) Diet vs. lifestyle, (2) Absolutism, (3) Social justice, and (4) Animal justice. These four themes represent how participants had differing perceptions of veganism according to their personal experience and understanding of the term. It appears participants took less of an absolutist approach to the definition and how individuals conceptualise veganism may be more dynamic than first expected. This will be important when researchers are considering how we are defining veganism in future studies to maintain consistency in the field.