Over the last two decades, the concepts of defence and security have overlapped to the point where the former is merged with the latter. Since jihadist terrorism broke out at the dawn of the millennium, governments have been forced to review the classic paradigm according to which the military is employed in overseas operations—or the defence of the homeland from external enemies—and police and law enforcement agencies are tasked with internal security. In such a context, the military has taken on an increasing role in national security matters, although security itself is an umbrella concept under development that currently includes such cross-cutting topics as terrorism, cyber threats, health, food, energy, the economy, poverty, climate change, information technology, social security, job security, just to mention a few. The inclination to replace the idea of defence with security has contributed to the expansion of the idea of security itself. This way, defence activities abroad, such as military assistance to Ukraine in the context of the ongoing conflict with Russia, are presented to the public as "security" operations. Well-established and reputable dictionaries such as Merriam-Webster, Britannica, Collins, Oxford, Cambridge, Longman, and Macmillan provide similar definitions of the term "security": safety; safety from attack, harm, or damage; freedom from danger or threat; freedom from fear or anxiety; being safe and free from worry; being protected or safe from harm. Security is the protection from, or resilience against, the potential harm caused by others by restricting one's freedom to act. In addition to these definitions, some of which are more focused on the person and his concerns and fears, there is a more comprehensive idea that incorporates the term “defence”. The definitions given by several dictionaries in this respect are pertinent. Therefore, according to the Cambridge Dictionary, security is the "protection of a person, building, organization, or country against threats such as crime or attacks by foreign countries". A similar definition is provided by the Oxford Dictionary: "the safety of a state or organization against criminal activity such as terrorism, theft, or espionage". On the same line, Longman says: "things that are done to keep a person, building, or country safe from danger or crime". These definitions show how the nature of the concept of security is changing, incorporating that of defence into much broader domains than the military realm. The term "defence", is given as a synonym of "security" by the majority of these dictionaries (Merriam-Webster, Cambridge, Oxford, Collins), even though Britannica and Macmillan continue to be anchored to the dichotomy of defence/external and security/internal, respectively, by providing the words "national security" and "internal security", is evidence of this trend. The evolving concept of security must be scrutinised, with special attention paid to the notion of human security, boosted by UN General Assembly resolution 66/290 and the NATO Strategic Concept 2022, and currently under investigation by the Exploratory Team of the NATO Science and Technology Organization.

This study was supported by the Ministry of University and Research (MUR), Italy, through the Young Researchers-Seal of Excellence grant funded by NextGenerationEU under the National Recovery and Resilience Plan

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