From Social Patterns
I prefer the term Direct Sharing to Private Sharing partly in recognition of the fact that nothing contributed to an internetworked data system is ultimately private in any meaningful, dependable way. Rather than viewing things through the lens of the age-old public-private dichotomy, it may be more fruitful to think in terms of many overlapping public spaces, some of which are more public than others.
In any given system, there may be a range of possibilities, from objects that are freely viewable to any passer-by, to items restricted to viewing only by (logged-in, authenticated) members of the community, to those that can be seen only by those included in a formal group or only those explicitly invited.
We consider any kind of sharing that isn't directed at an individual or a specific defined list of individuals to be public sharing. This form of sharing can be active, as when a user affirmatively posts content or information to a site for view and comment by friends, followers, fans, family, the general public or any other such audience. It can also be passive, as when activities are tracked and reported in an ongoing basis, generating update notices to friends or items in activity streams without requiring that the user consciously and deliberately share the activity or object.