Predicate calculus refers to a mathematical system used to represent reasoning and arguments using logical predicates and variables. However, there are various synonyms for this term, including first-order logic, quantificational logic, and predicate logic. All these terms refer to the same concept, which is a formal system used to express statements in a clear and logical manner. While predicate calculus is often associated with mathematics and computer science, it is also used in other fields such as philosophy and linguistics to represent complex ideas and arguments. Ultimately, this system allows us to make precise and accurate statements about various phenomena and situations.