A follower of one of the Eastern Catholic Churches. These churches are doctrinally Roman Catholic, but their ritual practice is a continuation of Eastern Christian practice (Eastern Orthodox, Oriental Orthodox, and the Church of the East).
Byzantine Catholic in particular refers to a follower of a church that is doctrinally Catholic, but whose ritual is derived from the Byzantine rite Eastern Orthodox church. The Eastern Catholic Churches also include practitioners of other rites—West Syrian, East Syrian, Armenian, and Alexandrian.
The Eastern Catholic Churches churches are commonly known as Uniate, but the term has been rejected by the followers as derogatory. By far the largest congregation of Byzantine Catholics is the Ukrainian Greek Catholic Church; runners up are the Melkite Greek Catholic Church and the Ruthenian Catholic Church.