Surface Metrology Guide - Filtering: "A surface profile may be composed of a range of frequency components. The high frequency (or short wave) components correspond to those that are perceived to be rough and hence called 'roughness'. The low frequency (or long wave) components correspond to more gradual changes in the profile and are often associated with the terms 'waviness' or even 'form'. Note that roughness and waviness are relative terms, just as the words 'high', 'low', 'long' and 'short'. "