UV Mapping is:

Is a way of saying u,v texture coordinates, which are positions within an ideal image (1-by-1). These typically connect to points in a 3D mesh, to position an image texture on the mesh. Like virtual tacks, they pin an exact spot on an image to a point on an object's surface. Between the tacks, renderers will stretch the image smoothly. This is what is referred to as UV mapping. UV mapping is used extensively in real-time environments, like OpenGL and typical 3D games, where hardware-based shading routines can be re-used for texture interpolation. It is also useful on another level with NURBS, and other parametric surfaces, which have inherent u,v parameters defined continuously along the entire surface.