A more thorough explanation:

Definition: An ally is a country or person that is connected to another country or person through a treaty or alliance. It means they work together and support each other.

Examples:

• The United States and Canada are allies because they have a treaty that says they will help each other if there is a threat to their security.
• During World War II, the United States and Great Britain were allies and fought together against Germany and Japan.
• John is an ally of Sarah because he supports her in her campaign for student council president.

The examples show how countries and people can work together and support each other through alliances. In the first example, the United States and Canada have a treaty that says they will help each other if there is a threat to their security. This means they are allies and will work together to protect each other. In the second example, the United States and Great Britain were allies during World War II and fought together against a common enemy. In the third example, John is an ally of Sarah because he supports her in her campaign for student council president. This means he is working with her and helping her to achieve her goal.