The Label distribution section with your Audience report is divided into two sections.
Inbox - reveals the top subjects your users talked about the most. This is based on labels you apply on users' comments, messages and posts (received in the Inbox).
Publishing - reveals the top subjects or topics you posted the most about. This part is based on labels you apply to your posts/content/tweets.
To get this report, you need to label your users' posts, comments or messages (here's how to do this manually and here's how to automate this using the Inbox Assistant feature) or your own Page's posts.
You can choose to display either:
a pie chart with all labels or;
only the top 10 labels for each part
Hovering your mouse over the given label will tell you how many posts, comments and/or messages have been marked with a given label.
Note: Inbox labels will be displayed in the reports based on the day the item was created, not when the label was applied.
Note: A post containing multiple labels will be counted for each label.