The term "Siegfried Line" typically refers to a German defensive line built during World War II. While it is a well-known phrase, there are several synonyms that can be used in its place. One such synonym is "Westwall," which was the official German name for the line. Another option is "Hindenburg Line," which refers to a similar defensive line used by the Germans during World War I. Alternatively, the term "Maginot Line" is often used to describe the French defensive line built before World War II. Regardless of the phrase used, all refer to fortified lines designed to protect against enemy invasion.