Original: The "Colours of Saint George", or St George's Cross are a white flag with a red cross, frequently borne by entities over which he is patron (e.g. the Republic of Genoa and then Liguria, England, Georgia, Catalonia, Aragon, etc.).
Simplified: The flag of England is white with a red cross. The design of the flag is often called 'The Saint George Cross', or 'The Colors of Saint George'.