When I tag someone in a post or photo, who can see it?
When you tag someone, that content (example: photo, post) may be shared with the person tagged and their friends. This means that if you haven't already included their friends in the audience, their friends may now be able to see it. For example, if you tag Jane in a photo shared with your friends, the audience expands to Friends (+) to include your friends and Jane's.
If you don't want your photo, post or other content to be visible to the friends of the person tagged, you can turn this setting off for each post when you post it. To do this, click the audience selector next to the story, select Custom, and uncheck the Friends of those tagged box.
The audience also expands to Friends (+) when others tag your post or photo. Learn how to approve or dismiss tags that friends add to your posts before they appear on Facebook.