The terms abrasion and erosion mean different things to various people. Moreover, there are many devices for measuring the response of materials to abrasive wear. The results from such machines do not consistently agree with those of the others because variables that differ in kind and amount are involved.Classification areas that help define the variables are an aid to the selection and application of laboratory and service tests. To three categories previously proposed by the author, and widely adopted, four others are now added for completeness and in hopes that misapplication of the terminology will be minimized. These are described and in several cases linked to better known laboratory tests.Of the categories: clean fluid erosion, impingement-erosion, erosion (as a simplified term) meaning parallel-flow low-stress abrasion, gouging-abrasion and erosion-corrosion; most attention is given to parallel-flow erosion because it seems most pertinent to the abrasion problems of automotive engineers and it is at present the focus of the SAE committee work with rubber-wheel erosion tests.A suggestive check-list of variables to be identified and described when reporting abrasion tests is provided.