A person who is too fat for typical clothing stores, but too thin for plus-size clothing. For women, this is typically between size 14-20, with some exceptions depending on the store.
A woman or man that does not fall into the category as fat or skinny. In other words, the perfect body shape.
List of celebrity examples. Scarlett Johansson, Jennifer Aniston, Jake Ggyllenhaal, Beyonce, Britney Spears, Brad Pitt, Bradley Cooper, Gerard Butler, Reese Witherspoon, Nina Dobrev, Paul Wesley, Ian Somerhalder, and so on and so on.. all are inbetweeny.