A defense system refers to a set of measures and strategies put in place to protect something or someone from harm, danger or loss. It can be applied to various contexts such as national security, computer systems, personal safety, among others. In terms of national security, it typically involves military forces, weapons, and surveillance systems that work together to safeguard a country's borders, infrastructure, institutions, and citizens from external threats like invasion or attack. At the individual level, one may have a home security system with measures such as alarms, locks, and cameras to protect their property and family from intruders. In computer systems, it refers to software programs that prevent unauthorized access, detect and remove malware, and ensure data privacy and integrity. Overall, the term defense system conveys a sense of readiness and preparedness in anticipation of potential risks or dangers.