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The term Prince of the Church is today used nearly exclusively for Catholic cardinals. However, the term is historically more important as a generic term for clergymen whose offices hold the secular rank and privilege of a prince or are considered its equivalent. In the case of cardinals, they are always treated in protocol of Catholic countries as equivalents of royal princes.
Informally, other members of the higher echelons of the Church are in recent times also occasionally called "Princes of the Church", in which case this title can sometimes be intended more or less ironically by the speaker.
By analogy with secular princes, in the broad sense of the ruler of any principality regardless of the style, it made perfect sense in a feudal class society to regard the highest members of the clergy, mainly prelates, as a privileged class similar to the nobility, ranking just below or even above it in the social order; often high clerical ranks, such as bishops, were given high protocollary precedence amongst the nobility, and seats in the highest assemblies, including courts of justice and legislatures, such as: