Semi-Formal
If you're getting invited to something that says semi-formal, it's either your sorority's annual event, prom, or you're attending a family member's sweet 16. Similar to black tie optional, but more forgiving, you can go long or short or opt for color-coordinated separates a la a full midi skirt and matching top.
Elizabeth and James Brendan Sleeveless Crop Blouse, $265; intermixonline.com
Tibi Silk Faille Full Skirt in Sapphire, $525; tibi.com