Lochs and firths aren't a breakfast food but rather geographic features. Lochs and firths are bodies of water. Both are formed by glaciation. Both loch and firth are Scottish words. Firths are long narrow arms of the sea. A loch is a lake but can also be a nearly landlocked inlet of the sea. Firths are river-fed estuaries. Lochs are not. Firths are similar to fjords. Lochs are much like fjards. Firths are found principally on the east coast of Scotland. Lochs are found mainly in the north and west.