Salisbury Steak and cube steak are essentially the same thing except in the way they are processed.
Cube steak or cubed steak is a cut of beef, usually top round or top sirloin, tenderized and flattened by pounding with a meat tenderizer.
The name refers to the shape of the indentations left by that process.
This is the most common cut of meat used for the American dish chicken fried steak.
Salisbury steak is a dish originating in the United States and made from a blend of ground beef and other ingredients and usually served with gravy or brown sauce.
It is a version of Hamburg steak.