Defence is a term used to describe the PROTECTION of a person, place, or thing. An ALIBI is an excuse used to prove that someone was not present at the time of a crime or other event. PROTECTION is the act of shielding something from harm or danger. GUARD is the action of watching over something to protect it. A MOAT is a deep, wide ditch filled with water that surrounds a castle or other structure. A BASTION is a fortified structure that provides PROTECTION from attack. Finally, AEGIS is a shield or PROTECTION given by a powerful person or organization. Together, these terms all refer to the concept of defence, which is the act of protecting something from harm or danger.