Any post on a social networking site (typically a puzzle, optical illusion, political question, inspirational story, etc.), that asks for the user to share it with friends on the site, with the supposed objective of getting as much exposure or attention as possible. Similar to the "you will die if you do not repost this comment x number of times" posts also seen frequently on social networks.
"Peggy, stop sharing every piece of sob-story sharebait you see on Facebook. It's fake and it's been circulating for years."