Per Wikipedia:

An ethnic group or ethnicity is a category of people who identify with each other, usually on the basis of presumed similarities such as a common language, ancestry, history, society, culture, nation or social treatment within their residing area. Ethnicity is often used synonymously with the term nation, particularly in cases of ethnic nationalism, and is separate from but related to the concept of races.

Ethnicity is usually an inherited status based on the society in which one lives. Membership of an ethnic group tends to be defined by a shared cultural heritage, ancestry, origin myth, history, homeland, language or dialect, symbolic systems such as religion, mythology and ritual, cuisine, dressing style, art or physical appearance. Ethnic groups often continue to speak related languages and share a similar gene pool. By way of language shift, acculturation, adoption and religious conversion.