What does the red stand for in united kingdom flag?

The red in the United Kingdom flag represents the cross of Saint George, the patron saint of England. The flag of England is a red cross on a white background, and it is one of the three flags that make up the Union Jack, the flag of the United Kingdom. The other two flags are the flag of Scotland (a white cross on a blue background) and the flag of Northern Ireland (a red cross on a white background).