An assertion is a claim that one believes to be true, while an axiom is a universally accepted statement that serves as a foundational truth for further reasoning. Axioms are agreed upon by a group to explore logical consequences, whereas assertions do not require consensus. The distinction lies in the level of acceptance and purpose in logical frameworks. Assertions can vary in validity, while axioms are established to provide a basis for mathematical or philosophical systems. Understanding this difference is crucial for engaging in logical discussions and analyses.