Security has many dimensions, depending on the situation. People secure boats by tying them to a dock, secure loans from financial institutions, or secure promises with a handshake. People feel less secure, or insecure, when they doubt their own abilities, when they lose their privacy, when a thief steals their wallet or purse. Thus, security is a psychological as well as a physical state of feeling—as well as being—protected from loss, breach of trust, attack, or any real or perceived threat.

The word security is widespread and appears in many contexts, from the United Nations Security Council and the nuclear and environmental security councils worldwide to national security, social security, and neighborhood security watch groups formed to keep homes safe from burglars. The term has become enshrined as well in the Department of Homeland Security, which describes itself as working "to keep America safe" with one...