For you to make the switch to digital TV.
and if you haven't done so - you'd better.
Remember, if you are a cable or satellite subscriber, you are set.
If you have a digital-ready set or a converter box, you are also set.
If not, and you still rely on analog TV, you'd better do something or you will lose your signal today.
Here are some links for more info:
FCC's DTV Site
So if you're not with the program - get moving!