What is a "Civil Emergency Message"?

-I have u-verse where you can dismiss the alert and it said Civil Emergency Message and my dad dismissed it. I don't know what it's about right now but I live in Dearborn, MI. What does this mean?I am not sure but they are probably to warn the city and my state in the event of an actual emergency.
I don't have an answer but I'm so glad someone else asked. I live in Westland and it keeps going off on my tv too. I'm hoping it's just a fluke because nothings on the news