Definition: The term Catholic is derived from the Greek word catholicos, "universal," and was initially adopted by Christians in the second century to distinguish themselves from the many and varied Christian sects that had begun to branch off from the original religion. As Christianity evolved, and especially once the ecumenical councils addressing matters of doctrine began, the term was less-frequently used. Whenever a sect departed from traditional teachings or from doctrine that had been accepted as "orthodox," or correct, the sects were deemed heretical, or "wrong," by the Church leaders. It was correctness that concerned them, not universality (which they accepted as a given).
Today the term Catholic is occasionally applied to medieval Christians in western Europe to distinguish them from Orthodox Christians in the east. However, medieval Christians would not have called themselves Catholics; they would have called themselves "Christians." Only after the Protestant Reformation of the 16th century would Christians find it necessary to declare whether they were Protestants, who followed one of the new religions that had broken away from the old Church (which Protestants viewed as corrupt), or Catholics, who accepted the ancient creeds and were members of the old Church (which Catholics viewed as the one "true" church).
