The esports market has been growing exponentially has been growing exponentially with much interest from industry and academia. Perhaps because of this growth, there is a lack of agreement on what esports actually encompasses. We conducted a systematic review of 461 peer reviewed, full papers that provide a definition of esports. Findings highlighted the growth of the esports field across different domains, and increasing global interest in esports, but a lack of consensus regarding definition of the term. Through thematic analysis we identified nine dimensions across esports definitions. We critically assess these dimensions in terms of their representativeness and utility in describing the multifaceted nature of esports. Our work may help create a shared understanding of what esports is- and is not-capturing a diversity of experiences within organized competitive gaming and supporting continued research growth in this increasingly important domain.