Providing more personal information than is absolutely necessary. Typically done when two or more people are conversing and details of one's sexual life creep into the discussion - or overly gross and disgusting details are included. Sometimes used in reference to loud cell phone users.
"dude, you know how like when I eat eggs and it gives me this horrible gas? Well, like I really had to go and I couldn't sit down on the toilet seat because the last guy left some crap on the seat and so I didn't want to touch it so I hovered and it came out and hit the wall and..."
Friend: "Dude, that's oversharing."
An exclamation in response to one who has pinned the meter on exposing too much personal information, usually to a group of people not commonly interwoven with one's personal life and activities.
"Did you hear Fred relate his Friday night encounter at today's meeting? Definitely Oversharing!"
When an individual decides to give more details about a certain event then what is actually needed.
I talked to Chris today. He really is good at over sharing the details of what he did last night