There are several synonyms for "a bomb shelter", a term that usually refers to a structure designed to protect people from the blast and shock waves of a nuclear explosion. Some of the alternative phrases include fallout shelter, blast shelter, bombproof shelter, emergency bunker, and nuclear shelter. These structures come in various types and sizes, ranging from underground bunkers to above-ground structures fortified with thick concrete walls and reinforced steel doors. Each type has its own set of advantages and disadvantages, depending on the local terrain and the expected threats. But regardless of the type, the underlying purpose of these shelters is to provide a safe haven for people in the event of a catastrophic attack.