NationBuilder has two note types. The first is a public note that you can post to someone's public profile. It will be visible to everyone.
The second is a private note for administrators. It is part of NationBuilder's social CRM and will appear in the dashboard activity stream.
You can also display one private note prominently in the administrative view of a person's profile. This is the background note at the top of a profile and can be used to keep track of important information about donors and supporters or to exchange background information between nation admins. Simply click where it says "Add background..." to add a background note to a profile that doesn't have one.