These are nights when all 3 restaurants serve the same menu. There are several web sites where you can view the menus.
There are 3 nights when the restaurants each serve their signature menu--thus, on those nights, each restaurant will be serving different food. However, since you would normally rotate thru all 3, you will have a chance to experience each one.
Then on the "themed" nights (like Captain's Gala, pirate, etc.) all 3 serve the same food. Is this clear as mud? I sometimes don't explain things well.