What is an announcement? What is a sticky post?
 

Announcements contain important information posted by the administrator. They are a simple one-way communication with the users and not a discussion thread.
Announcement threads are displayed globally at the top of forum , above regular and sticky threads.

Sticky threads are created by moderators or administrators, and remain stuck to the top of the listing. Their purpose is to keep important information visible and accessible at all times in specific forums. Sticky threads are not global.