This character is seen wearing a bunny costume/dress.

The two essential part of the dress are the bunny ears (usually in the form of a headband) and the bunny tail tailored to the lower back of the dress.

The form of the costume itself can vary, depending on its nature. In case of a sexy dress, it can be a leotard, or just underwear. In case a dress aimed for children (like for a masquerade) can be pyjama-like in design, covering the entire body.