Union Jack

Union Jack (plural Union Jacks)

The Union jack of the United Kingdom. Flag Ratio: 1:2

1. The flag of the United Kingdom, consisting of the flags of England (St. George's Cross), Scotland (St. Andrew's Cross), and Ireland (St. Patrick's Cross) now only used in Northern Ireland combined.
   • 20 May 2018, Hadley Freeman in The Guardian, Is Meghan Markle the American the royals have needed all along?

     When the wedding started I found a spot near Windsor Castle’s entrance, where I could watch the ceremony on a big screen. People who line the roads at weddings are, by definition, the most die-hard royalists, and all the usual figures were out in force: the men bellowing and ringing bells in the hope of convincing a passing American TV crew they are an actual town crier; the men in suits made of Union Jacks.

2. (nautical, Britain) The flag, consisting of the flags of England, Scotland, and Northern Ireland combined, flown on ships of the government of the United Kingdom.
   

   US Union Jack
3. (nautical, US) The flag, consisting of the blue star-studded field in the corner of the national ensign, flown at the jackstaff by ships at anchor[1].

The Union Jack (also Union flag, union jack) is regarded as the official flag of the United Kingdom, although technically no law to that effect has ever been passed.