Yes they were code names as others have said. The main two purposes are security (no need to refer to specific places that might then be more easily discovered) and for planning (you can plan a lot in relation to a specific area without need of specific detail). read more
Omaha, commonly known as Omaha Beach, was the code name for one of the five sectors of the Allied invasion of German-occupied France in the Normandy landings on June 6, 1944, during World War II. read more