Wedding dress code

Never heard of it and after a Google, the only thing I could think of regarding wings would be wing collar shirts. You typically wear them with a bow tie so it could be formal black tie, just with a more confusing name. I would suggest your friend asks to be certain because a lot of people won't have a black tie outfit.

Think it is a collar. Hop onto Google and type in wing colour images

Maybe it means penguin suits, like wings.

Don’t let her stress! This is a fun, whimsical dress code—wings are usually small fairy/angel-style accessories and waistcoats are formal vests to match outfits. It’s a quirky twist to keep the vibe playful yet fancy, no need to ask the bride!