Spatial arrangement of the gray or color levels of the pixels in a region of an image with distinct regularity, periodicity or randomness

Form A. K. Jain, Fundamentals of Image Processing: "The term texture generally refers to repetition of basic texture elements called texels. The texel contains several pixels, whose placement could be periodic, quasi-periodic or random. Texture may be coarse, fine, smooth, granulated, rippled regular, irregular, or linear."