Surface roughness, often shortened to roughness, is a measure of the texture of a surface

Surface

In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...

. It is quantified by the vertical deviations of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small the surface is smooth. Roughness is typically considered to be the high frequency, short wavelength component of a measured surface (see surface metrology

Surface metrology

Surface metrology is the measurement of small-scale features on surfaces, and is a branch of metrology. Surface primary form, surface waviness and surface roughness are the parameters most commonly associated with the field...

).

Roughness plays an important role in determining how a real object will interact with its environment.