A generic term applied to certain potentially difficult or stressful affinal (‘by marriage’) secondary relationships in extended families. These relationships are, to a differing degree in different societies, subject to strain—either because of the potential for (threatening) sexual relations or because of lack of a specified role content for incumbents. Typically, strain is avoided by physical avoidance; by codifying the relationship so that it is subject to minute regulation of correct behaviour and precise requirements; or by ‘personalization’, whereby the parties involved are expected to create a working relationship, merely on the basis of their own goodwill and personalities. The custom takes many forms. Among the African Galla, for example, a man must not mention the name of his mother-in-law, drink from a cup she has used, or eat food prepared by her, although he can address her directly.
Where this custom of maintaining a respectful distance between certain relatives occurs, there is also frequently associated with it a directly contrary relation of familiarity, usually called a ‘joking relationship’. Thus, a man might have an avoidance relationship with his wife's parents, but a joking relationship with her brothers and sisters.