There are different types of breakfast - Continental, Fruit Basket, Fast-food, High-Fiber, and other special breakfast sets. While they are mostly based on regional or cultural preferences, there are breakfast items that are common across all types such as coffee and bread (it’s the variety of bread that differs).
Casual breakfast are breakfast sets that is not so elegant or ‘proper’ nor too informal (despite it being called ‘casual’).
Summary:
Samples of casual breakfast menus and compared with other breakfast sets