An announcement was a public notification or declaration of an important activity or event that everyone in a community or in an organization should know.
In 2364, while discussing about Kurt Mandl concealing something, Counselor Deanna Troi said to Captain Jean-Luc Picard, "He is concealing something. It's more than just being too busy. Your announcement about coming down has sent him almost to a point of panic." (TNG: "Home Soil")