A ribbon is a thin band of flexible material, typically cloth but also plastic or sometimes metal, used primarily for binding and tying. Often seen used in elaborate clothing and hair. May be tied into any sort of knot, often a bow. In general it also have to be long and narrow.
post #844003: On top of her hair that should be consider a ribbon. The ribbon tying the hair tails together however should be consider a bow.
source: danbooru wiki