Abrasion means that the top layers of the skin (the epidermis) are mechanically eroded via friction. This can occur with spanking and shows in skin areas that are "raw" or sore, like a rug or carpet burn.
These areas will become sticky to touch due to the emmission of lymph (wound exudate). There can also be light bleeding. Deep abrasion is also known as excoriation, while light abrasion is also known as graze.