Texture refers to the surface quality, both simulated and actual, or artwork.
Techniques used in painting serve to show texture.
For example, the dry brush technique produces rough simulated quality and heavy application of pigment with brush or other implement produces a rough actual texture.
Texture in Fine Art
Rouault painted this painting in oil paint with heavy textures. The painting technique that emphasizes actual texture is called impasto. Such textures can be applied with a stiff brush or spread on the canvas with a painting knife.
Simulated textures occur when smooth painting surfaces appear to be textured.
Source: Elements and Principles of Design: Student Guide with Activities, published by Crystal Productions