Some ḥadīth experts understand the terms ḥadīth, khabar (report), and athar (trace, vestige, relic) as synonyms. Others distinguish between khabar as any transmitted knowledge (or a historical report in particular), ḥadīth as a tradition about the Prophet, and athar as a report about the Companions and Successors.
Pavlovitch, Pavel, “Ḥadīth”, in: Encyclopaedia of Islam, THREE, Edited by: Kate Fleet, Gudrun Krämer, Denis Matringe, John Nawas, Everett Rowson. Consulted online on 17 July 2018