When you holler, you shout very loudly, often so someone far away can hear you. It is a strongly American word. A person might holler for help, holler a name across the street, or holler because they are hurt or angry. It sounds informal, and a little rough or country; you would not holler in a quiet office. Though actually, it is not always an angry word. A parent can holler “Dinner!” from the kitchen, and friends can holler a happy greeting. You can also call the shout itself “a holler.” Older English had calls like holla, hallo, and hollo — ways of shouting to someone. Holler is the American shape of that. Hello grew from the same kind of call, but hello became the polite greeting, and holler stayed the loud shout.