What term is defined as conduct prejudicial to good order and discipline, which undermines the senior's authority?

The term that accurately describes conduct prejudicial to good order and discipline, which undermines the senior's authority, is insubordination. Insubordination involves any action or behavior that shows a lack of respect for authority, particularly when a subordinate refuses to obey a lawful order from a superior. This behavior directly challenges the established hierarchy and can disrupt the cohesive functioning of a military unit, which relies on a clear chain of command and respect between ranks to maintain discipline and effectiveness.

While fraternization refers to inappropriate relationships between ranks that can also affect discipline, it does not specifically address the refusal to obey orders. Discipline breach is a more general term that may encompass various forms of misconduct but lacks the specificity of insubordination. Command misconduct typically pertains to actions or failures of leadership that go against policies or regulations, rather than direct disobedience to authority.