Course News Items
A special forum called "News" appears in the "weekly" and "topics" course formats. It's a good place to post notices for all students to see. (By default, all students are subscribed to this forum, and will receive your notices by email.)
This setting determines how many recent items appear on your course home page, in a news box down the right-hand side.
If you set it to "0 news items" then the news box won't even appear.