What does that mean for you? Free food! But only if you dress up as a cow. Or at least partially like a cow...
Specifically, on Cow Appreciation Day, any person who walks into a Chick-fil-A dressed up as a cow will receive a free meal (entree, side, drink) of their choice. If you're not ready to go full cow, you can just wear a cow accessory (like a cow shirt, tie, hanky, etc.) and get a free entree of your choice.
If you're looking for ideas (or just want to see what's it all about), you can check out the Chick-fil-A Cow Appreciation Day website for pictures of last year's participants.