Announcements are grouped by a topic which can then be used as a Filter on the newsfeed. You can assign a topic when you create an announcement, or change and assign a topic when you edit an existing announcement.
By default there are five topics:
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You can add more topics by clicking Add new, and edit the existing ones by clicking on the pencil icon.
Topics can be ordered by dragging them using the arrows icon. The order of Topics in the table influence the order in which topics appear on top of the newsfeed.