Dressy casual may seem like a confusing dress code, but its really quite simple. It's about dressing up what you'd wear casually. Think about what you may wear to church or a work meeting. Not quite as casual as jeans, but not so fancy you have to wear a 3-piece suit, or a floor length dress.

Here's a general dress code overview:

https://www.cosmopolitan.com/style-beauty/fashion/a30474742/dressy-casual-dress-code-meaning/

For the guys that need some ideas or extra descriptors(because Tristan was also confused):

https://www.friartux.com/blog/blog2291.html?srsltid=AfmBOoruXpLTBoEgpEhCvcPsUHtkNiUCU396YGh3Fox-HHp8A9hJH_h_