Insubordination is the act of willfully disobeying one's superior. Refusing to perform an action that is unethical or illegal is not insubordination; neither is refusing to perform an action that is not within the scope of authority of the person issuing the order.
Insubordination is generally a punishable offense in hierarchical organizations which depend on people lower in the chain of command doing what they are expected to do.
Insubordination is when a serviceman or servicewoman wilfully disobeys the lawful orders of a superior officer. If a military officer were to disobey the lawful orders of his or her civilian superiors, this would also count. For example, the head of state in many countries, is also the most superior officer of the military as the Commander in Chief. (see Civilian control of the military) Generally, an officer or soldier may be insubordinate to the point of mutiny if given an unlawful order, however. (see Nuremberg defense)
In the U.S. military, insubordination is covered under Article 91 of the Uniform Code of Military Justice. It covers disobeying lawful orders as well as disrespectful language or even striking a superior. The article for insubordination should not be confused with the article for contempt. While Article 91 of the UCMJ deals predominately with disobeying or disrespecting a superior and applies to enlisted members and warrant officers, Article 88 involves the use of contemptuous words against certain appointed or elected officials and only applies to commissioned officers.