The skin on your knee and elbow is often referred to as “skin over the joint” or more commonly, “flexural skin.” This skin is different from other areas because it is thicker and more resilient to friction, as these joints are frequently in motion. The skin around the elbow and knee also has folds or creases that allow for movement when these joints bend.
Additionally, in the context of the body’s anatomical regions, the skin covering the knee is sometimes specifically called the patellar skin (patella being the kneecap), and the skin over the elbow can be referred to as the olecranon skin (olecranon being the bony prominence of the elbow). However, these terms aren’t used very commonly in everyday language.