A more thorough explanation:

Definition: An army is a group of people who are trained and equipped to fight in wars or battles. It can also refer to any large group of people who are organized and working towards a common goal.

Examples:

• The United States Army is a branch of the military that is responsible for ground warfare.
• The rebel army fought against the government forces in the civil war.
• The company's marketing army worked tirelessly to promote their new product.

The first two examples illustrate the military aspect of an army, where trained soldiers are organized and equipped to fight in wars or battles. The third example shows how the term can be used metaphorically to describe a group of people who are working together towards a common goal, in this case, promoting a new product.