Ethnicity is a term used to differentiate among groups of people according to cultural expression and identification. It is essentially self-defined and may change over time. Ethnicity has been defined as "the social group a person belongs to, and either identifies with or is identified with by others, as a result of a mix of cultural and other factors including language, diet, religion, ancestry, and physical features traditionally associated with race". Ethnic membership tends to be defined by a shared cultural heritage, ancestry, origin myth, history, homeland, language, dialect, religion, mythology, folklore, ritual, cuisine, dressing style, art, or physical appearance. Ethnic groups may share a narrow or broad spectrum of genetic ancestry, depending on group identification, with many groups having mixed genetic ancestry. Ethnicity is often used interchangeably with the term nation, particularly in cases of ethnic nationalism. The standard classification of ethnic group in the UK is that used in the 2011 Census, which was slightly different in each of the four countries of the UK. Ethnicity is a broader term than race, which refers to the concept of dividing people into groups on the basis of various sets of physical characteristics and the process of ascribing social meaning to those groups.