XXI is the Roman numeral representation for the number 21. Roman numerals are a numeral system originating from ancient Rome, using combinations of letters from the Latin alphabet. In this system, "X" represents 10, and "I" represents 1, so "XXI" combines two tens and one unit. The number 21 holds significance in various cultures and contexts. For example, in many countries, turning 21 is associated with reaching the legal drinking age, symbolizing the transition into adulthood. Additionally, in games, 21 is often associated with the popular card game Blackjack, where players aim to reach a total of 21 points.