I've often wondered about American salads.
To me, anything named "salad" had to have some sort of lettuce in it. Here, mayo seems to be key in order to call something a salad.
Sure, there are salad bars and menu options that offer "the regular:" lettuce, tomato, cucumber, peppers... perhaps some mushrooms... But, if you go to a restaurant and order "tuna salad" or "chicken salad," it means the tuna or chicken is mixed with mayo, celery and some spices and eaten on toast. Chicken salad as I know it doesn't exist.
It's a mystery to me.