A salmon burger is a type of fishcake

Fishcake

A fishcake is a food item similar to a croquette, consisting of a filleted fish and potato patty sometimes coated in breadcrumbs or batter, and fried. Fishcakes are often served in British fish and chip shops....

 made mostly from salmon

Salmon

Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

 in the style of a hamburger

Hamburger

A hamburger is a sandwich consisting of a cooked patty of ground meat usually placed inside a sliced bread roll...

. It is challenging to make and cook as the salmon requires a binder to make it stick together and is easy to overcook which makes it too dry. Salmon burgers are especially common in Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

where they are routinely offered as an alternative to beef hamburgers.