enclaver

To enclose a piece of land entirely within another's territory, leaving it landlocked or without its own direct access — a legal and geographic term you'll meet in property law (un terrain enclavé) and in descriptions of small countries surrounded by a larger one.

• Ce terrain est enclavé, sans accès direct à la route. — This plot of land is landlocked, without direct access to the road.
• Le Lesotho est entièrement enclavé dans l'Afrique du Sud. — Lesotho is entirely enclosed within South Africa.
• Les urbanistes ont enclavé le quartier entre deux voies ferrées. — City planners hemmed the neighborhood in between two rail lines.

The adjective enclavé(e) (landlocked, hemmed in) is what learners meet constantly in geography and real-estate contexts — the conjugated verb itself is rarer, but means exactly the same enclosing action.