When an invite states "festive attire" which means attire that isn't so casual as t-shirt and jeans but more formal than casual or work attire. Festive attire is supposed to stimulate an enjoyable, sexy, party atmosphere. Think sequins, beading, ruffles, bows etc. The host want visitors to decorate stylish stylishly. Anything you put on should cause you to feel pretty and sexy, so that you will be prepared to dance and have fun. Destination wedding ceremonies demand elegant although not too formal dresses. You may decide to choose something totally different from the typical dress. Particularly if you are seeing a beach wedding, you will want to feel special and outfitted-up while still island-appropriate.