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Stepmother from WikiPedia:

Traditionally, a stepfamily is the family one acquires when a parent enters a new marriage, whether the parent was widowed or divorced. For example, if one's father dies and one's mother marries another man, the new man is one's stepfather and vice versa. The counseling slogan "Stepfamilies are born out of loss" applies to such a case.

In modern stepfamilies, there is recognition that the biological parents may never have married. Unless one biological parent of a stepchild is deceased, typical nuclear stepfamilies do not live in one house, consisting of three or more parents, biological and otherwise. It is also possible, in a less strict sense, that the new mate chooses the role of full- or part-time caregiver without marital commitment. However, it is generally understood that after a child reaches adulthood, a parent's subsequent marriage does not create a stepparent relationship unless the various parties choose to regard it as such.[citation needed]

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