An oversharer is a social media addict who shares too many things on social networks according to his social media relations.
Oversharing is mainly met on Facebook and Tweeter.
There are two dimensions of hoversharing:
sharing two many incidental events
sharing things which are judged as too personnal for sharing
In the latter case, oversharing may be accidental. In the first case oversharers are very active but not necessarily good influencers.