This is the flag of the United Kingdom of Great Britain and Northern Ireland, the British flag, also known as "the union flag", which consists of a dark blue background and red and white "+ / X" characters. It is displayed as EN on some platforms. It generally means Britain, British, or within the United Kingdom, and its capital is London.
🇬🇧 is the Emoji of a country/region‘s flag, and its meaning is flag: United Kingdom. The Emoji 🇬🇧 is composed of two regional indicator letters, namely 🇬 and 🇧. The country/region's 2-letter code for United Kingdom is GB, so the letters corresponding to the two region indicator letters are G and B. 🇬🇧 is displayed as a whole flag on most platforms and as a two-letter symbol on a few platforms.