A more thorough explanation:

Direct aggression is a term used in international law to describe a serious violation committed by a nation. It refers to the use of armed force by a state against the sovereignty, territorial integrity, or political independence of another country, or in a manner inconsistent with the Charter of the United Nations. This type of aggression involves a state's regular armed forces participating in military operations.

For example, if Country A sends its army to invade Country B, it would be considered direct aggression. This type of aggression is a crime under international law, and aggressors can be held accountable for their actions.

It is important to note that there is no generally accepted definition of what constitutes aggression, despite many attempts over the years to devise one. However, the United Nations General Assembly adopted a Resolution on the Definition of Aggression in 1974, which provides some guidance on the matter.

Direct aggression is different from indirect aggression, which involves delictual acts carried out by means other than a state's regular armed forces. Examples of indirect aggression include economic pressures, demands couched in traditional diplomatic terms but laden with implied threats, and aiding and abetting of rebel bands intent on overthrowing another government.

Overall, direct aggression is a serious violation of international law that involves a state's regular armed forces participating in military operations against another country.