Ponchos are, fundamentally, large single pieces of cloth with a hole for the head cut out that are worn over the shoulders. With that in mind, that's probably the best term for it (I know I certainly haven't been able to think up an alternative outer garment that fits the bill as well.)
Traditional ponchos usually extend over the shoulders simply because they were originally a more utilitarian piece of clothing, but modern ones are known to take more liberties with sizing and whatnot. Ico's is just more of a..uh, fashion poncho, I suppose.
Does that pose have a name or something? I saw the identical pose, but in a Final Fantasy XIV setting where Ico is replaced by a miqo'te spout and Yorda by a viera mentor.
