Waldorf salad was invented at the very end of the 19th century in New York’s Waldorf Hotel.  Originally it was just celery and apple, dressed well.  Over time other ingredients have been added - walnuts (or pecans), grapes, blue cheese, leaves such as watercress and sometimes chicken breast.  To be quick, you could use shop-bought mayonnaise, or plain yoghurt flavoured with mustard and lemon juice.