A stepfamily or blended family is a family where at least one parent has children, from a previous relationship, that are not genetically related to the other parent. Either one or both parents may have children from a previous relationship. Children from a stepfamily may live with one biological parent, or they may live with each biological parent for a period of time. In addition, visitation rights mean that children in stepfamilies often have contact with both biological parents, even if they permanently live with only one.
A child is referred to as the stepchild, stepdaughter or stepson of their biological parent's new spouse, and that person as the stepparent, stepfather or stepmother of the child.
A stepfather is the husband of one's mother and not one's biological father. A stepmother is the wife of one's father and not one's biological mother. Similarly, a stepbrother is the son of a stepparent who one is not biologically related to. A stepsister is the daughter of a stepparent to whom one is not biologically related. A parent's spouse of the same sex may also count as a stepparent.
Alternatively, in Australia Under the Family Law Act 1975 (Cth) a ‘stepparent’ in relation to a child, is interpreted as a person who is not a parent of the child; and is, or has been, married to or a de facto partner of, a parent of the child; and treats, or at any time while married to, or a de facto partner of, the parent treated, the child as a member of the family formed with the parent.
The traditional and strictest definition of a "stepfamily" is a married couple where one or both members of the couple have pre-existing children who live with them. More recently, the definition is often expanded to include all cohabiting couples, whether married or not. Some people also apply the term to non-custodial relationships, where "stepparent" can refer to the partner of a parent with whom the child does not live. The term is not generally used (but can be in individual cases) to refer to the relationship with an adult child who never lived in the home with the parent's new partner.
A "simple" stepfamily is one in which only one member of the couple has a prior child or children and the couple has not yet had additional children. When both members of the couple have at least one pre-existing child, the new family is "complex" or "blended" from the start; if only one member has one or more prior children but the couple has another child together, the "complex"/"blended" designation replaces the "simple" designation upon the birth of the new child. If both members of the couple have prior children, those children are stepbrothers and stepsisters to one another. Any subsequent child born to the couple is a half-sibling of the respective members' prior children.
If a stepparent legally adopts the partner's child or children, he or she becomes the child's legal parent. In such cases, the parents may stop using the terms "stepparent" and "stepchild" and instead refer to the child simply as their son or daughter; depending on the child's degree of affinity for the adoptive parent and/or approval of the legal proceedings culminating in the child's adoption, the child may likewise drop the "step-" designation from his/her description of the relationship. Even when all parties describe the relationship using the terms applied to biological and adoptive families, however, at least some of the emotional and psychological issues common to stepfamilies may persist.