"In sociology, an ethnic enclave is a physical space with high ethnic concentration; thus these spaces are culturally distinct from the larger receiving society. Their success and growth depends on self-sufficiency, and is coupled with economic prosperity. Therefore, the general definition of an ethnic enclave is a geographically defined space with characteristic cultural identity and economic activity. The term is usually used to refer to either a residential area or a workspace with a high concentration of ethnic firms." - Wikipedia
Basically, an ethnic enclave is a group of people who all share the same ethnicity living and working in an area, usually maintaining traditions. A great example of this would be China Town in California.