I remember quite some time ago when I would ask various Catholic friends of mine if they were Christians. Sometimes they would respond, "No, I'm Catholic." This served to further reinforce the notion I had then that Catholics were not Christians. Unfortunately, those individuals didn't understand their own faith. For Catholics are most certainly Christians. In fact, they were the first Christians.
After the ascension of our Lord, the early believers were known by a number of names such as those "of the way", or simply as the "brothers". We read that it was in Antioch in Syria that the believers were first called "Christians" (Acts 11:26). In the early second century we begin to find references to the Catholic Church. This was a way of distinguishing the true Church from heretical sects. While heretics held many things in common with the Church, it had its distinctives that separated it from her. But the Church held the same faith throughout the world.
The term, "Catholic" means universal, or general. It came into use to describe the faith of the whole Church throughout time and space. Eventually it came to also indicate that the whole faith was intact without additions or subtractions. This was the same faith they had received from Jesus and the apostles.
Today there are many different kinds of Christians. That is, there are many different denominations and even independent groups of Christians. When someone describes himself as a Catholic Christian, he is saying that he holds to the faith as it was once for all delivered to the saints. He believes and worships according to the most ancient form of Christianity there is.
Today we are still a long way from the unity that God intended to characterize all Christians. We still have great misunderstandings about one another. It is my hope and prayer that this situation will change in the very near future. I hope that all Christians can come together in love and believe that same faith that was originally given by our Lord and His apostles. I hope that we can humbly join together in this faith. Then we would all truly be Catholic Christians.