Could be any height, could be plus size, or petite, could be any ethnicity. Models are not just one standard thing these days.
However, a model isn't a model until she has modeled for something. Modeling just your self doesn't make you a model. Being pretty doesn't mean you are a model. A model works with brands and products to sell the image or tell the story of the brand with their look or physical assets. They are all sizes and it is just the media that talks most of fashion, when actually print modeling, which covers a vast diversity of models, is the biggest area of the modeling business and advertising world.
Also, I think the Internet in many ways has dismayed and ruined the word model.