This study aims to examine students' perception of the term used to label cyberbullying, the perception of different forms and behaviours (written, verbal, visual, exclusion and impersonation) and the perception of the criteria used for its definition (imbalance of power, intention, repetition, anonymity and publicity) in three different European countries: Italy, Spain and Germany. Seventy adolescents took part in nine focus groups, using the same interview guide across countries. Thematic analysis focused on three main themes related to: (1) the term used to label cyberbullying, (2) the different behaviours representing cyberbullying, (3) the three traditional criteria of intentionality, imbalance of power and repetition and the two new criteria of anonymity and publicity. Results showed that the best word to label cyberbullying is ‘cyber-mobbing’ (in Germany), ‘virtual’ or ‘cyber-bullying’ (in Italy), and ‘harassment’ or ‘harassment via Internet or mobile phone’ (in Spain). Impersonation cannot be considered wholly as cyberbullying behaviour. In order to define a cyberbullying act, adolescents need to know whether the action was done intentionally to harm the victim, the effect on the victim and the repetition of the action (this latter criterion evaluated simultaneously with the publicity). Information about the anonymity and publicity contributes to better understand the nature and the severity of the act, the potential effects on the victim and the intentionality.