Cyber harassment differs from cyber stalking in that defined as NOT involving a credible threat.
Cyber harassment usually pertains to threatening or harassing email messages, instant messages, or websites dedicated solely to tormenting an individual.
Cyberbullying is when a child, preteen or teen is tormented, threatened, harassed, humiliated, embarrassed or otherwise targeted by another child, preteen or teen using the Internet, interactive and digital technologies or mobile phones.
It has to have a minor on both sides
Cyber stalking is the use of the Internet, email or other electronic communications to stalk, and generally refers to a pattern of threatening or malicious behaviors.
Cyber stalking considered the most dangerous of the three types of Internet harassment, based on a posing credible threat of harm.
Further Readings
The following link provides both friends and parents information on Cyberbullying.