The concept of 'audience' is central to research and practice in science communication. When asked by a scientist for help communicating their work, who among us has not responded with the time honoured question 'who is your audience?' Yet what we mean when we talk about audience is not always clear: implied and ambiguous, rather than explicit and precise. This article explores this ambiguity, drawing on a systematic review of 1360 science communication research articles and a survey of 45 science communication educators. We report 10 different conceptualisations, in three groups. Being conceptualisations include 'Demographic', 'Knowledge', 'Values' and 'Embodied'; Doing conceptualisations include 'Interaction' and 'Dynamic'. In Qualifiers, we found 'Diverse', 'Potential', 'Plural' and 'General' conceptualisations. These data allow tracking of how we have conceptualised audience over time, an understanding of the groups systematically under-serviced, and a pathway to a richer discussion of this key concept for our field.