An enclave is a nation or a part of a nation that is completely within another nation. Some examples of this are San Marino and Vatican City, both which are entirely within Italy and the small country of Lesotho, which is completely within South Africa.
A semi-enclave is an enclave which is almost completely surrounded by another country, where the remaining border is a body of water. Gambia, Monaco, and Brunei are semi-enclaves.
Enclaves differ from exclaves.