According to experts discussing cyberbullying in an awareness campaign, which of the following is a defining characteristic of cyberbullying?
A) It is always a single, isolated incident of online harassment.
B) It primarily involves physical harm caused by online interactions.
C) It is limited to private messages and never occurs on public platforms.
D) It involves repeated, intentional harm inflicted through electronic devices.
E) It only occurs between adults and never involves teenagers.