Formal wedding attire sits between cocktail and black tie on the wedding dress code scale. It's slightly more elevated than cocktail attire and a touch less dressy than black-tie nuptials.
Formal wedding attire (similar to black-tie optional attire) offers a bit more flexibility than black tie, so ankle-length dresses and dressy separates are acceptable, as well as fitted, darker-hued suits paired with a crisp white button-down and tie.