In recent years, both the media and academia have examined the expansion and social impacts of companies collectively referred to as Big Tech. From privacy and democracy to the encroachment into sectors such as finance, health and education, numerous empirical and conceptual studies have investigated this influential group. Surprisingly, far less attention has been paid to clarifying what “Big Tech” actually is and formulating a theoratical definition. Through a systemic review of 230 academic articals, we show tha the concept is defined inconsistently: few works offer intensional definitions (what Big Tech is), while many rely on extensional lists of specific companies. Futhermore, both definitions types vary widely. The lack of a shared framework risks fragmenting research into disciplinary silos and hindering comparative studies. A common definition would not only enhance scholarly dialogue but also support more effective regulation by delineating the boundaries of Big Tech.