Effective worldwide efforts to conserve flora and fauna rely on engaging the public, and thus on public appreciation of the object of conservation activities (most commonly, 'biodiversity'). We examined alignment of interpretation of the term 'biodiversity' with generally accepted definitions in a representative sample (n = 499) of the public from the State of Victoria in Australia, a country with an explicit biodiversity conservation strategy (which defines the term) and the capacity to invest heavily in conservation. However, almost half of respondents did not know what 'biodiversity' meant, 32% and 18% expressed an ecological and conceptual interpretation, respectively. The probability of having at least some interpretation of the term was higher among university-educated respondents, but otherwise did not vary with sex or income. Broadening the base of conservation efforts would likely be facilitated by better aligning interpretations of the term 'biodiversity' among the public or by adopting more intuitive language when engaging with the public.