Let me clear up some of the terminology used in Stepfamily literature:

Stepfamily—A household in which there is an adult couple, at least one of whom has a child by a previous relationship. This includes households where the children live most of the time and households in which the children are seldom present. It include households in which adults have a committed relationship but are not legally married, and it includes same-sex couples who have come together after one or both have had a child.

Stepmom/Stepdad—The new partner of the child’s biological parent. This adult is not biologically related to the child.

Bioparent—he biological parent of the child; a child usually has two biological parents.

Stepcouple—A biological parent in a relationship or married to another partner, who now is the Stepparent.

Residential parent—The parent with whom the child or children live most of the time. Usually it’s the parent who has primary custody.

Nonresidential parent—The parent with whom the child lives less than the majority of the time.

Children in Stepfamilies are referred to as:

Siblings—Biologically related; from the same parents

Stepsiblings—Not biologically related; parents are married to each other.

Half-siblings—Partially related biologically (i.e., share one parent).

Mutual Child —A child born to the Stepcouple.