overshare (verb): to divulge excessive personal information, as in a blog or broadcast interview, prompting reactions ranging from alarmed discomfort to approval.
The most common alternative term is Too Much Information (TMI).
Don't go searching for overshare in your Webster's New World Dictionary just yet. Editor-in-chief Mike Agnes explains:
Typically words chosen as Word of the Year are parts of emerging English. They’re not yet in. They don’t have a track record of usage. They don’t have a breadth of usage yet that qualifies them for entry in the dictionary. But they are words that we’re watching with our language monitoring program.
Over at Visual Thesaurus, Ben Zimmer analyzes the winner and its "rather more idiosyncratic" runners-up (leisure sickness, cyberchrondriac, selective ignorance, and youthanasia). Note: this article may be behind a paywall; email me if you need assistance.