A more thorough explanation:

An enclave is a term used in international law to describe an isolated part of a country's territory that is entirely surrounded by the territory of another country. This means that any communication with the main part of the country must pass through the territory of the foreign country. Enclaves are relatively rare nowadays, but some examples include:

• Baarle-Hertog: a Belgian enclave in the Netherlands
• Kaliningrad: a Russian enclave between Lithuania and Poland

Another type of enclave is a federal enclave. This refers to territory or land that a state has ceded to the United States. Examples of federal enclaves include military bases, national parks, federally administered highways, and federal Indian reservations. The U.S. government has exclusive authority and jurisdiction over federal enclaves.

Finally, there is the quasi-enclave. This is an isolated part of a country's territory that, although not entirely surrounded by the territory of a foreign country, is inaccessible by way of the country's own territory because of topographical features such as impassable mountains.

Overall, enclaves are unique geographical features that can have significant political and legal implications for the countries involved.