Incest is sexual intercourse between close relatives that is illegal in the jurisdiction where it takes place and/or is socially taboo. The type of sexual activity and the nature of the relationship between people that constitutes a breach of law or social taboo vary with culture and jurisdiction. Some societies consider incest to include only those who live in the same household, or who belong to the same clan or lineage; other societies consider it to include ""blood relatives""; other societies further include those related by adoption or marriage.