An enclave is a territory entirely surrounded by another territory.
An exclave is a territory legally or politically attached to a main territory with which it is not physically contiguous because of surrounding alien territory.
These are two distinct concepts, although many entities fit both definitions. In Fig. 1 at right, suppose that the darker shaded area (marked B and C) is part of the same political or territorial entity, for example a sovereign state, and that the lighter-shaded area marked A is another such entity. Then C is an exclave of B, and is also an enclave within A. If C were independent it would be an enclave but not an exclave. In Fig. 2 at right, C is again an exclave of B, but is not an enclave, because it has boundaries with more than one entity.