Somebody, usually a model, who has a stick-instect, gamine figure and therefore can fit into super-trendy clothes in tiny sizes. If they are a model, they change their clothes frequently and always look cool (in the fashion world, at least).
"Kate Moss is such a clothes horse. I wished I looked as good as her..."
A person who is passionate about new clothes. A big shopper and consequently, a big spender.
Suzy is a real clothes horse!