<p>Bullying has been studied for over 50 years, and research on the topic has been extremely fruitful. Nevertheless, there are still important inconsistencies in definitions used in research on bullying and cyberbullying, which negatively impact research, policy and practice. Among other problems, varying definitions can cause underreporting and overreporting of bullying in different contexts. Thus, the current mixed-methods study was conducted to propose definitions of bullying and cyberbullying based on the opinion of the scientific community in the field worldwide. The study included 149 bullying and cyberbullying researchers from 36 different countries. Proposed definitions are based on a qualitative free definition provided by the participants and a quantitative part focused on different elements of the definitions. Based on our findings, we propose that bullying could be defined as a repeated violent behaviour perpetrated with an intention to harm, that causes physical, social or emotional harm to a victim who cannot defend themselves given an imbalance of power. There are bullying roles such as victims, perpetrators and bystanders. Cyberbullying could be defined as bullying perpetrated through electronic devices, within a social network by known and unknown people. These definitions are useful to guide bullying research, policy and practice.</p>