A mermaid dress is a style of evening gown that fits closely to the body through the torso and hips, then "fishtails" out in a flare to the floor. (This is why it's also known as a fishtail dress.)
A trumpet silhouette is a perfect midway point between a fit and flare gown and a mermaid dress, as the skirt flares lower down than a fit and flare to highlight more of your curves, but isn't as dramatic or restrictive as a mermaid.
Walk in a wedding dress with good posture, keeping the shoulders back and stomach tucked in. Pick up the wedding dress and hold it slightly off the ground when walking with instructions from a bridal shop consultant in this free video on wedding dresses.