A more thorough explanation:

A federal enclave is a piece of land or territory that a state has given to the United States government. Examples of federal enclaves include military bases, national parks, federally administered highways, and federal Indian reservations. The U.S. government has complete control and authority over these areas.

For example, the Guantanamo Bay Naval Base in Cuba is a federal enclave. It is a piece of land that the United States leases from Cuba, but the U.S. government has complete control over the area. Another example is the White Sands Missile Range in New Mexico, which is a military base that is also a federal enclave.

These federal enclaves are important because they allow the U.S. government to have exclusive control over certain areas that are important for national security or other purposes. They are also subject to different laws and regulations than the surrounding areas, which can sometimes cause conflicts between the federal government and the state or local governments.