The term asbestos has been defined in numerous publications including many State and Federal regulations. The definition of asbestos often varies depending on the source or publication in which it is used. Differences in definitions also exist for the asbestos-related terms acicular, asbestiform, cleavage, cleavage fragment, fiber, fibril, fibrous, and parting. An inexperienced reader of the asbestos literature would have difficulty understanding these differences and grasping many of the subtleties that exist in the literature and regulatory language. Disagreement among workers from the industrial, medical, mineralogical, and regulatory communities regarding these definitions has fueled debate as to their applicability to various morphological structures and chemical compositions that exist in the amphibole and serpentine groups of minerals. This debate has significant public health, economic and legal implications. This report summarizes asbestos-related definitions taken from a variety of academic, industrial, and regulatory sources. This summary is by no means complete but includes the majority of significant definitions currently applied in the discipline.