The word "vegetarian" usually appears in food, restaurants or recipes, and is used to refer to vegetarian or vegetarian food, such as "vegetarian burger", "vegetarian stir-fry dish" and "vegetarian lasagna" (vegetarian lasagna).
"veggie" is not only the abbreviation of "vegetable", but also can be used to describe things related to vegetables, such as "vegetable garden" and "vegetable pizza".