Many Sydney families use the words baptism and christening interchangeably, and in most everyday contexts that is perfectly fine. But there is a subtle theological distinction worth understanding.
Baptism
Baptism is the sacrament itself. The ritual of water and the formal admission of a person into the Christian faith. It applies to people of all ages, from infants to adults.
Christening
Christening traditionally refers specifically to the naming of a child at the time of their baptism. The word comes from giving the child their Christian name. In modern usage it has become synonymous with infant baptism.
In Practice
For photography purposes, the ceremony is the same regardless of which word you use. Tinyfoot photographs both Catholic baptisms and Anglican christenings across Sydney, and the approach is identical for each.