St. David (UK) flag 90 x 150 cm
The Flag of St David is normally a yellow cross on a black field, although it appears in many forms including a black cross on a yellow field, or with an engrailed cross. It has been used as a flag representing Wales (as an alternative to the Red Dragon flag), in the same sense that the crosses of St George, St Andrew and St Patrick are used to represent England, Scotland, and Ireland (of which they are, respectively, patron saints). It is similar, and no doubt related, to the arms of the Diocese of St David's. It is not to be confused with the Saint Piran's Flag, the Cornish flag, which is a white cross on a black field.
source: Wikipedia