Everything that's posted on Facebook, whether it's an update, a photo or a comment, has its own independent privacy setting. That means a friend could make one photo album public and another visible only to close family members. The content you can see on your friends' Timeline pages and in the news feed is determined by all of these different privacy settings working together.
The Audience Selector
Whenever you upload or post something to Facebook, you'll notice an audience selector tool that enables you set the privacy level for that content. Various options are available, including Public (anyone can see the content) and Only Me (only you can see it). You can limit the item's visibility to friends, or a custom list of friends and contacts, but not acquaintances. The same audience selector option is available to every Facebook user, and this is why you might not be able to view everything someone else does on the site, even if you are friends.
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