Brexit is the term used to describe the United Kingdom's (UK) withdrawal from the European Union (EU), a political and economic union of 27 European countries. The term is a portmanteau of "Britain" and "exit," and it gained widespread usage following a referendum held in the UK on June 23, 2016. In that vote, 52% of the British public chose to leave the EU, initiating a complex and contentious process that involved years of negotiations between the UK and EU to determine the terms of their separation. Issues like trade agreements, citizen rights, and the status of the Northern Ireland border were among the most challenging aspects of the discussions. The UK officially left the EU on January 31, 2020, entering a transition period that lasted until the end of the year. Brexit has had broad implications on multiple fronts—economically, politically, and socially—both within the UK and across Europe. Its long-term effects continue to unfold, affecting everything from international trade to immigration policies.