An increasingly influential strand of research on social media relies on the concept of affordances to account for effects. However, hindering the possibility of a unified theory of affordances in social media is the conceptual blurring surrounding the concept. This article engages in a comprehensive review of the affordances literature in social media, aiming to provide an overview of the current state of the art and clarify the use of the concept. Through a systematic literature review, the characteristics of affordances research in social media are uncovered: the most prominent areas of application, research approaches, and dominant typologies and conceptualisations. Significant blurriness of the term ‘affordance’ is identified as well as an inconsistent use in research. To tackle these problems, a unified definition of affordances in social media is proposed based on the synthesis of knowledge on affordances in technology and social media. The suggested definition captures the core aspects of the concept to reduce ambiguity in the use of the concept and further the research on affordances of social media. The article provides the groundwork for future use of affordances theory in social media research.