a knight without a liege; a mounted soldier belonging to no particular order or having no sovereign; lack of affiliation to a house; so named as they have no permanent home, having to sleep outdoors i.e. under a hedge.
Usage: 'Hedge knights had an unsavory reputation. "A hedge knight and a robber knight are two sides of the same sword", it was said.' George R. R. Martin - A Feast for Crows