The apple is characterised by hips, waist and shoulders being of a similar width. This is often (but not always) combined with slender, toned arms and legs. The majority of any weight gain will occur around the middle.
Liv Tyler, Emma Bunton, Judy Finnegan (of Richard & Judy fame) and Mikyla Dodd (from Hollyoaks and Celebrity Fit Club) are just some of the celebs that an apple will share their shape with.
When it comes to getting an outfit for the Wedding, apples should consider dresses that help to define the waist - a typcial example would be to opt for a bodice accompanied by an A-line skirt. A bodice with a dropped waist, or a traditional bodice that comes down to a point, are particularly flattering. Detailing around the bust will pronounce that area and dresses that feature a high bust line (such as one with an empire line top) made from a loose flowing material will also flatter your shape.
For very slim apples, dresses in a bias cut profile are good for creating the illusion of shape, but it is probably worthwhile avoiding dresses with fish-tail skirts as these will not bring out the best in your figure. Similarly, it is difficult to create definition between waist and hips with the ultra-straight skirt of the column dress, so again this may not be your best bet.