'Family' is a single word, with many different meanings. People have many ways of defining a family and what being a part of a family means to them. Families differ in terms of economic, cultural, social, and many other facets, but what every family has in common is that the people who call it a family are making clear that those people are important in some way to the person calling them his family.
A family is a group of two or more people that are related by blood, marriage, adoption, step or fostering, and who usually live together in the same household. This includes newlyweds without children, gay partners, couples with dependants, single mums or dads with children, siblings living together, and many other variations. At least one person in the family has to be over 15.