If someone is bandy-legged, their legs curve out at the knees, so there is a gap between the knees when the feet stand together — an O shape, not an X. People also say bow-legged, which is more common in everyday talk; bandy-legged sounds a little older or more like a book. It describes the shape of the legs. Said kindly, it is just a body shape, often from childhood or from a lot of riding. The other way, knees that knock inward, is knock-kneed. Bandy on its own can mean the same thing: bandy legs.