A more thorough explanation:

Definition: A federal instrumentality is a means or agency used by the national government. It can also refer to a national agency or entity that is immune from state control.

Examples:

• The United States Postal Service is a federal instrumentality that is responsible for delivering mail and packages throughout the country.
• The Federal Reserve System is another example of a federal instrumentality. It is responsible for regulating the nation's monetary policy and ensuring the stability of the financial system.

These examples illustrate the definition of a federal instrumentality because they are both agencies that are created and controlled by the federal government. They are not subject to state control and are responsible for carrying out important functions that affect the entire country.