When people are talking in Christian terms about a “denomination,” what is the definition that most are using for the word denomination? What are they calling a denomination?
de·nom·i·na·tion, n.: 1. A large group of religious congregations united under a common faith and name and organized under a single administrative and legal hierarchy (source: Dictionary.com).
Generally speaking, the word denomination is used to classify a particular Christian sect within the overarching Christian religion. For Catholics, using the word denomination for the Catholic Church is inappropriate because the Church is not one Christian sect among many. The Church is the visible religious body founded by Jesus Christ to teach, spread, and administer the Christian religion.
Handbook of Denominations** by Frank S. Mead