A measure of the variation of the intensity of a surface, quantifying properties such as smoothness, coarseness and regularity. It's often used as a region descriptor in image analysis and computer vision.
The three principal approaches used to describe texture are statistical, structural and spectral. Statistical techniques characterise texture by the statistical properties of the grey levels of the points comprising a surface. Typically, these properties are computed from the grey level histogram or grey level cooccurrence matrix of the surface.
Structural techniques characterise texture as being composed of simple primitives called "texels" (texture elements), that are regularly arranged on a surface according to some rules. These rules are formally defined by grammars of various types.
Spectral techiques are based on properties of the Fourier spectrum and describe global periodicity of the grey levels of a surface by identifying high energy peaks in the spectrum.