What part of the mass had unchanging text regardless of the calendar date or festival?

The part of the Mass that had unchanging text regardless of the calendar date or festival is the "Ordinary." This includes key prayers and responses such as the Kyrie, Gloria, Credo, Sanctus, and Agnus Dei. Unlike the "Proper," which varies according to the liturgical calendar and specific celebrations, the Ordinary remains consistent throughout the liturgical year.