Macaroni Salad is macaroni mixed with vegetables and mayonnaise, very similar to American macaroni salad.  Because Japanese mayo has a very different flavor from mayo in the US, Japanese Macaroni Salad tastes quite different, just like Japanese Potato Salad.  It is a very good side dish for Yoshoku (western style dishes) such as Hamburger Steaks and Menchi Katsu.