Roma place great value on the extended family. Even in urban areas and among highly assimilated Romani families, the extended family, or tsigni vitsa, is strong. Although they may live in separate homes, family members keep constant contact by telephone and daily visits. The extended family is an important economic unit and the base of a network of economic ties. Kinship for any individual may be reckoned bilaterally, although patriliny is usually the basis of membership in the larger vitsa (clan). A son may decide, however, to retain membership in his mother's vitsa, whereas a wife may take on her husband's. This flexibility is perhaps aided by the fact that Romani kinship terminology is cognatic (i.e., kinship links are not distinguished by gender)—father's sister and mother's sister are both called bibi, for example. Kinship terms may be used by younger people as forms of address for older people, and the converse is also true. Phral and pey (brother and sister) can be used as terms of friendship and greeting. Cousins ( worof ward ) are not distinguished by degree. Roma often use or are influenced by Russian terms, collapsing terms in usage (e.g., "second-line brother" for "cousin").