What is the difference between Catholic and Christian?

Catholics are Christians. A Catholic is a Christian who belongs to the Catholic Church and professes the faith, sacraments, and authority Christ entrusted to her.

What Christian means. The disciples of Jesus were first called Christians at Antioch (Acts 11:26). In ordinary Catholic usage, a Christian is someone who has received valid Baptism and professes faith in Jesus Christ and the Trinity. Baptism establishes a real sacramental bond among all who are reborn through it (CCC 1271). Catholics, Eastern Orthodox, and many Protestants are therefore Christians, although they are not all in full communion with one another.

What Catholic means. The word catholic means universal. The Catholic Church is the Church governed by the successor of St. Peter, the pope, together with the bishops in communion with him. Catholics receive Sacred Scripture and Sacred Tradition as one deposit of faith, recognize the Church's Magisterium, and profess seven sacraments, including the Eucharist as the true Body and Blood of Christ. The Church teaches that the one Church of Christ subsists in the Catholic Church, governed by Peter's successor and the bishops in communion with him (CCC 816).

How other Christians are related. Christians who are validly baptized but separated from full Catholic communion are joined to Christ and rightly recognized as brothers and sisters in the Lord (CCC 818). The Eastern Orthodox Churches possess apostolic succession and valid sacraments, especially the priesthood and Eucharist, but they are not in full communion with the pope (CCC 838). Protestant communities retain important elements of Christian truth and holiness, though their teachings differ from Catholic doctrine in varying ways concerning authority, sacraments, justification, Mary, and other matters.

Why full communion matters. Christian divisions contradict Christ's will that His disciples be one (Jn 17:20-23). The Church teaches that the fullness of the means of salvation is found in the Catholic Church. A person who knows that Christ founded the Catholic Church as necessary and deliberately refuses to enter or remain in her cannot be saved through that refusal (CCC 846). Those who, through no fault of their own, do not know Christ or His Church may still be saved by grace if they sincerely seek God and strive to do His will (CCC 847-848). God alone judges each person's knowledge and responsibility.

In practice. A Catholic should readily say, "I am a Christian, specifically a Catholic Christian." If you are a baptized non-Catholic considering Catholicism, attend Mass, begin learning the faith, and contact a parish about OCIA. Until you are received into full communion, refrain from receiving Communion except in the limited cases permitted by Church law.