The Union Jack is the national flag of the United Kingdom. It combines the crosses of three patron saints: St. George for England, St. Andrew for Scotland, and St. Patrick for Ireland. The flag features a blue field with a red cross edged in white, overlaid with a diagonal red and white cross. The design symbolizes the unity of these nations under one flag. The Union Jack is used in various official capacities, including on government buildings and military uniforms. It is also a popular symbol in British culture and is recognized worldwide.