Following the recent changes to the diagnostic category for addictive disorders in DSM-5, it is urgent to clarify what constitutes behavioural addiction to have a clear direction for future research and classification. However, in the years following the release of DSM-5, an expanding body of research has increasingly classified engagement in a wide range of common behaviours and leisure activities as possible behavioural addiction. If this expansion does not end, both the relevance and the credibility of the field of addictive disorders might be questioned, which may prompt a dismissive appraisal of the new DSM-5 subcategory for behavioural addiction. We propose an operational definition of behavioural addiction together with a number of exclusion criteria, to avoid pathologizing common behaviours and provide a common ground for further research. The definition and its exclusion criteria are clarified and justified by illustrating how these address a number of theoretical and methodological shortcomings that result from existing conceptualizations. We invite other researchers to extend our definition under an Open Science Foundation framework.