A tostada is often served as an appetizer topped —usually— with a thin layer of refried black bean paste, chicken or beef strips or other kinds of animal products (such as pickled pig's feet), thinly chopped lettuce strips, sour cream, and usually garnished with chopped onion and salsa.
In Tex-Mex cuisine, tostadas are often referred to as tortilla chips and are also served as an appetizer, without toppings, but with sauce or salsa for dipping.