A "dressy" warm up suit or sweat suit. It may be a little brighter and/or shinier than a person's everyday warm up suits, and it is reserved for special occasions. It is worn by someone who rarely dresses up, but who is truly making an effort by donning the holiday sweats.
Cousin 1: You're invited to a Christmas Party at my house.
Cousin 2: Great! What is the attire?
Cousin 1: Casual chic.
Cousin 2: Awesome. I will wear my holiday sweats.
Cousin 1: I expected nothing less... and be sure to wear your formal tennis shoes.