Unlike garlic salt or garlic powder, garlic pepper can feature a variety of ingredients. The simplest garlic pepper is a combination of ground black pepper and finely ground dried garlic. Many like this type as a great substitute for salt, because you get the wonderful seasoning of pepper added to the spiciness of garlic. You really do have to read the labels carefully, since this seasoning can have many more ingredients.
Sometimes garlic pepper is a combination of salt, ground garlic, pepper, and even brown sugar.