An incident which involves multiple frapists attacking a single Facebook account simultaneously. Gang frapes most notoriously occur when a 4chan user posts an announcement on /b/ that they have hacked the Facebook account of some person (most often a female) for whom they feel some form of displeasure.
The person posting will also encourage other users to join in on the attack, which inevitably leads to n00bs with un-stealthy tactics ruining the lulz for everyone by making it too obvious to casual observers what is actually happening. This is why gang frapes are innately fraught with fail.
A proper frape is carried out by an individual rather than a group, so that a more surgical (and therefore lulzy) strike can take place.
My mom announced on her FB that she was thinking about becoming a back ally abortionist in her spare time, but when I saw all the comments telling her to do it faggot, I realized that a gang frape was taking place