All Christians are Catholic.
Catholic comes from a Greek word which merely means "Universal", i.e. all Christians.
The group you're referring are Roman Catholics, the largest Christian denomination. The Roman Catholic Church is fairly similiar to most Orthodox branches of Christianity like Greek and Russian Orthodox; but it can differ greatly with some Protestant branches like Presbyterians, i.e. The Church of Scotland.
It has a lot in common with the Anglican branch though, i.e. The Church of England, The Church of Ireland and any Episcopalian Churches; which has lead some in recent times to believe that the rift between the Anglican Communion and the Roman Catholic Church may finally be healed, but I'd say this would take quite a bit of reforming on the part of the Vatican.
In some countries where Roman Catholics are not the largest Christian denomination, i.e. Scotland, they sometimes struggle for proper recognition. On the enrollment forms for my college, they even had "Roman Catholic" and "Christian" as two separate boxes under what your Religion was, implying that the administration did not see Roman Catholics as Christians.
But, simply put, Roman Catholics are Christians. One of many denominations.