Which of the following describes the term "under arms"?

The term "under arms" specifically refers to the condition of being equipped with a weapon, particularly in a military context. This includes the expectation that a military member is either wearing a sidearm or carrying a weapon as part of their duties or readiness for combat. The concept emphasizes readiness and the armed state of individuals within a military environment.

In contrast, simply being on active duty or walking unarmed does not fulfill the criteria of being "under arms," as these conditions do not involve the individual carrying or wearing a weapon. Additionally, while carrying a ceremonial sword may imply an armed status, it does not typically align with the standard interpretation of being "under arms," which signifies readiness for combat rather than ceremonial duties. Hence, the accurate description is indeed associated with wearing or carrying a weapon.