Much like salad in the US can have different vegetables and different sauces, Yum is a mix of meat and/or vegetables in a strong flavored sauce. While many people know of Yum Nua (Steak Salad), Yum dishes have a very broad set of ingredients and flavors.
Flavors
Yum dishes frequently have the maximum amount of flavor per bite of any Thai dishes.
Preparation Notes
You will want to maximize the flavor of each ingredient by, for example, cutting an onion in slices as thinly as possible.