From the Document: "The United Kingdom (UK) formally withdrew from membership in the European Union (EU) on January 31, 2020. Under the withdrawal agreement negotiated by the two sides, the UK is to continue applying EU rules during a transition period scheduled to run through the end of 2020. During the transition period, the UK and the EU are expected to begin negotiating the terms of their future relationship, including trade and economic relations as well as cooperation on foreign policy, security, and a range of other issues."
CRS Report for Congress, R45944
Congressional Research Service: https://crsreports.congress.gov/