Body shaming (BS) is a popular term for a type of negative social interaction, which frequently occurs in social media. However, there is a lack of a clear scientific definition of BS and data on its relation to other concepts in social aggression research. The present study therefore aimed at providing a definition and classification of BS. In an exploratory online-study, 25 participants (60%) provided personal definitions of BS and rated the fit of a suggested definition. In addition, they reported similarities with and differences to related concepts (appearance teasing, cyberbullying, trolling). We conducted qualitative analyses of the verbal definitions guided by the Grounded Theory approach and quantified the fit to existing concepts in the field of social aggression. The results show that BS is perceived as an unrepeated act in which a person expresses unsolicited, mostly negative opinions/comments about a target's body, without necessarily intending to harm him/her. Still, the target perceives the comments as negative. BS can range from well-meant advice to malevolent insults and it can occur online and offline. Participants saw similarities between BS and appearance teasing. BS can be a tool for trolling and can evolve to cyberbullying with repetition over time. Altogether, BS is a form of social aggression that has a negative impact on individuals. The definition and classification help to investigate BS and its effects on body image and mental health in future research.