There are about as many kinds of sausages as there are cuisines worldwide. As a simple version, breakfast sausage is distinct thanks to a few key flavorings.
Most breakfast sausages are made with specific herbs, such as sage or rosemary, and spices like cayenne. These contribute to a flavor profile of warm, woodsy flavors.
Maple syrup is also often used as an ingredient. That hint of maple sweetness sets this sausage apart from more strictly savory "dinner" sausages.
Breakfast sausage also has a looser structure than most "dinner" sausages. The meat is not rested for as long after salting, creating a sausage with a tighter texture.
Most breakfast sausage is also less emulsified than other options, which gives it a coarser texture.
Breakfast sausage is found in links and case-less patties, while other styles are defined by their shape. A bratwurst, for example, fits into a casing and is formed into links.