What are axioms or postulates?

Axioms or postulates are basic assumptions or self-evident truths that are accepted without proof or demonstration. In mathematics, they are the starting points or building blocks of a particular system or theory. Axioms serve as the foundation for mathematical reasoning and provide a framework for developing mathematical proofs and theorems. 

Euclid's Elements, for example, is based on a set of five postulates and five common notions, which together form the foundation of Euclidean geometry.