» For other uses, see Incest (disambiguation). For the biological aspect, see inbreeding. Incest refers to any sexual activity between closely related persons (often within the immediate family) that's illegal or a social taboo. The type of sexual activity and the nature of the relationship between persons that constitutes a breach of law or social taboo vary with culture and jurisdiction. Some societies consider it to include only those who live in the same household, or who belong to the same… (More on Incest)