The honest answer is this: Salami (sliced salami), pepperoni (sliced spicy salami), and sausage (pre-cooked fennel-flavored uncased/crumbled pork sausage).

In the US, “sausage” tends to generically refer to uncured, fresh, or raw sausages, often really meaning “ground meat mixed with herbs and spices sometimes in a tube or casing (but not always).”

Is it like the Italian American "shrimp scampi" where it's just the words for shrimp in two different languages? My understanding is that "salami" is just the Italian word for cured sausage.

Also, "pepperoni" is an Italian American word for a spicy salami that contains peppers, so it's just a type.

In Italy, pepperoni would be peppers then wouldn’t it?